I have experience making content for SL. With the exception of textures and animations SL does not import anything, everything is made in world. All avatars are based on two basic models which are morphed, similar to Poser figures. (This doesn't include avatars with 3d prop attachments which are made in world)

Most clothing in SL is just trans mapped textures applied to clothing layers built into these base models.

Poser can be used to make animations... (Walks, dances... ahem... other things...) You Make your anim then export a BVH for upload to SL, but that is about the extent of synergy between the 2 programs.