I don't really know much about it at this point, but can't you unwrap anything in Blender to make a UV map? I think it might be redundant to include in MB Lab.z

As for the A-pose/T-pose thing, it does seem odd it auto-reverts in one window but not another. I think, however, that the A pose might be better for setting up clothing that's not t-shirt-like in its behavior, like a suit jacket, for instance, because the deformation of non-stretchy clothing is compression when moving the arms up, not stretching when you move the arms down. However, I'm not that far along yet, and could be talking out of my *.