That is a question you should be asking yourself, especially if you have a partner, in which case ask her.
There is also the question of what is in it for the lady whose nudes you are asking for - is she a potential partner or just a bit of fun on the side?
In my experience most ladies would not like their partner watching porn but it would not be a deal breaker, some may even be amused by it and watch it with you but getting close enough to another real live woman to ask for nudes would get your eyes scratched out.