Yes it can be done but moisture is a major concern. If the basement stays dry, humidity can be controlled, you have a good vapor barrier between the OSB and the concrete and the OSB is sealed (polyurethane etc.) then I would do it. I would just let the homeowner know the possible problems before agreeing to install it.

It is a really big waste of labor for a basement. Since labor is the lion's share on any install, it doesn't cost that much more to use something that won't rot when exposed to the typical moist basement slab. Like vinyl tile or porcelain tile.

I hope she is talking about the OSB covering on the DriCore subfloor panels? If not, then she should be looking at building a sleeper subfloor (with vapour barrier underneath) and then 2 layers of subfloor. The last layer being OSB.

DriCore states you can finish the top of their subfloor systems with a few coats of poly. True. You still have to do some sanding and some cleaning ($0.50/sf) and then you need 2-3 coats of polyurethane ($1/sf). If she adds a stain = $0.30/sf more. Labor is going to be extra. By the time it is all said and done...with labor etc, she would be better off with a $0.79/sf laminate and $0.40sf cork underlay...it will be the same price and she doesn't have to wait for the finish to cure (10-30 days depending on the finish).

OSB can have several coats of poly applied to it. It will even take stain. Just remember to tell her that it will cost MORE to put a floor down over top of "finished" OSB than if she just put flooring down over it right now.

Not all floors will go over top of "finished" OSB. There are several types of installs that would require the "finish" to be covered up before being put down. That means her $2/sf per square foot "finished" OSB will cost MORE because she has to lay new plywood over it to get something else to sit over it.