I was thinking of buying some M4/V4 poses from Renderosity.com. Some of them are made for Poser. Will those work on Daz without any problem?
Yes they will work on any M4/V4 character you load into DS 4. That said, however, if you're using Genesis in DS 4, then I'm not sure if they will or not, as I haven't tried it.
You can still use them, but you're going to want this so they look right and you may still need to adjust a little.
I don't buy commercial V4M4 poses for Genesis because of the adjustment needs; if I'm going to have to do that anyway, there are tons of free ones (such as Structure's on Rendo Free Stuff, which are fantastic and numerous). I do buy DZheng's pose packs for Genesis and have used them frequently.