Genesis I and II are very low resolution meshes already, so they don't need LOD versions.

Yes, of course you can make a "native" Poser rig for a Genesis mesh, but you'd have to do it completely from scratch, joint centers and all.

And you'd have to make separate rigs for every major Genesis figure/morph like V5, M5, Julie, etc, as you can't easily extract all those "sub-rigs" from the main Genesis rig in Poser.

BTW, if you use Poser's own subdivision instead of Genesis' DSON subdivision, Genesis is not slow at all. (Except for the initial loading which is a bit slow).

But again you need Poser 10 or PP-2014 for that. and the newst versions of the DSON importer and the Genesis files.