The artifact in the foot looks like the spherical fall off zone needs to be widened, some of the polys are not being included.

You've already figured out the the import/ export process for the standalone Ivy Generator (or as a plug for various apps), it's just a matter of ironing out the bugs. The Ivy Generator requires an object composed of tri's as a support so from the get go I would say that V4 is a pretty unwieldy subject to convert to tri's for a support mannikin, essentially doubling the poly count (tried triangulating the blMilWom_v4b.obj in Carrara and it caused serious lag and a force quit, in wings triangulation increased the poly count from 68k to 149k). I would use a low poly blank .cr2 as a mannikin and donor. Using the default V4 .cr2 as donor has all kinds of magnets, morph channels, etc. that make it unsuitable as a donor rig (I'm assuming this is what you are doing).

You need to have a dedicated nuts & bolts modeler in your arsenal... like wings, hex, silo, etc. In wings if you select all objects composing your Ivy Figure and do an export selected of all as one .obj the object will appear in poser as a single object which can be dissected via materials or groups (I would leave all import settings unchecked). Upon import into Poser I can't see any reason why you would be losing the UV's on the .obj, if in fact the UV's are actually being lost. If so it has something to do with your export settings from the Ivy Generator.

Example: in a modeler I create a simple .obj and uv map it, assign a single material, and create a texture. I duplicate the uv'd object 10 times and export as a single object. I import this object into Poser, enter the material room and find my originally assigned material on the object, apply the texture and the texture is duplicated multiple times applied correctly to its composite parts. If I had assigned an individual material to all the parts in the modeler before exporting as a single object the Poser result would be a single object with multiple material regions.

As far as the disappearing planes that have the leaf materials, try flipping normals.

Hope these shots in the dark have been somewhat helpful.

ps. another method of object gluing would be to import all into poser and then re-export, selecting all parts from the hierarchy list (click the universe to uncheck all, tick the comprising parts), export as wavefront. Upon reimport your object will be consolidated.