I don't really understand the issue with "hair fits." It's not terribly difficult, but the nuances revolve around one major factor - Does the geometry involve only one group or multiple groups?

Note - That's "geometry", not "rigging." If the actual geometry is all one group, then no-problem, all the geometry morphs will be fine and it's easy to deal with. If it's multiple groups, things might be a bit tricky...

Most conforming hair is structured around Poser's native rigging deformer requirements in that they're generally all "neck" groups. (This way, all neighboring children in standard figures will contribute deformations during movement and there won't be an squirrely, messy, issues) Some may have separate groups but these are a rarity with exception for certain creators. And, in general with newer hairs, even creators who have multiple groups are not interfering with the intended figure's rigging or anything, they're just adding extra controls or have separated groups out for easy morphing and customization and they do not actually involve any assigned rigging. (ie: A scalp group just because, a hair group for all the controls, a internal name conforming "neck" group with all the "real" geometry for the main rigging group, etc...)

What I would do in order to make conforming hair fit a character's rig it wasn't intended for is pretty straightforward as long as it is one group:

(Trying to keep this inside of Poser as much as possible. In general, I'd take it out to several 3d apps.)

1. Using the dev or a properly zero'd version of the target figure, position the hair item, unconformed, and scale it to approximate fit. Use magnets and the morph tool to make it look good.

2. Export the geometry as a wavefront object file after you have finished it. (Save the scene, in case you need to make changes.) Export only the single group of geometry, every checkbox blank. All you need is this group, if it's a single group.

2a)This process is for renaming the group to match the figure's neck bone name, keeping within standard conforming hair conventions. If you can use Poser's cloth or grouping tool to do that, then use it. I prefer the easy way.

3. Rename the hair model's single group to the appropriate internal bone name for the target's neck rig. I choose to do this using a external 3D app or, easy-peasy, using UVMapper Lite to rename everything to one single group in a couple of clicks.

4)Import the hair object with the renamed group (or, get ready to use the one you've renamed, minus its rigging) and then take it to the Setup room. Here, you have two options - You can transfer the rigging of the intended target character (Not a great option) or you can use good rigging that is in a hair model you already have for that character (better option if this is for your own use). I generally use the latter.

Open up your content directory, go to the model who's rigging you're going to use, then doubleclick on it. It will prompt you if you want to set up renamed rigging zones based on the rig. Nope, not needed, everything is already named that you need to be named, since that model already has a neck bone rig for that figure. (I transfer rigging using a separate app, so forgive if I make an error describing the Setup room.) Remove any bones you don't want, but "ghost bones" in some hair rigs, as long as the entire geometry is still only one group, can be handy, so don't remove those unless you're sure you don't want them. As long as they are a child of the "neck" parent, they'll work eventually.

5. Back in the Preview mode, test and fine-tune your rig using the Joint Editor. You may have to scale some of the standard deformer zones and fine tune a few things so that all of the geometry in your hair conforms correctly. If you're having bad issues with "scaling" as in your base character's figure is scaled, it's often helpful to include a path of rigging all the way to the figure's focus, usually the hip. So, head+neck+collars(L&R)chest+abdomen+hip is a good solution for scaling issues with human rigs. Only the bones neighboring the neck are going to effect the hair model group "neck", but the rest help the conforming figure find it's appropriate centers during scaling if you have an issue.

And... what about morphs? No problem. You can transfer them, as long as you didn't regroup the object in the case of an object with mulitple groups, easy.

6. Using Poser Pro, you can probably transfer them within Poser. If you don't have Pro, then you can use the ancient freebie "Morph Manager" to transfer them. It still works just fine. Since you're only, in this case, transferring morphs in a single group, you won't have any issues.

On "prop" hair - Prop hair is there as an easy solution. In my experience, it's always just one group too. And, because of this, you can use it the same way in a conversion from "prop" hair to "conforming" hair.

On parented hair - Parented hair can really suck... especially when loading poses. I dunno, maybe it's ancient Poser conventions, but parented hair tends to get buggy and shoot all over the place. It also doesn't always like keeping its center of rotation. And, even if you try to dump magnets on it, random_old_pose_58 will bork it up. Them's the breaks. That goes doubly for parented, rigged, hair, since poses will sometimes try to apply the rotations to the hair for some weird reason. Sometimes, it's an easy fix of just loading up the Joint Editor and select "Zero Rotations." Sometimes it's not. That's why I never use any parented hair that isn't easily repositioned. (Short hair, easy, long hair, hard.)

In any case - If you can rename groups appropriately for the new rigging, then any hair can be used for any figure. Even unconventionally named groups are fine, just as long as you have the "real geometry" named correctly for the figure's neck/head/whatever bone that will be the primary parent rigging for the rest of the children. (neck, usually) Hairs with logical groups that point to no geometry or rigging may need extra care, depending upon what morphs/controls are in them.