My advice is a flat out no to be honest.
There's so much risk of your friend finding out and you can't even do the old "Ah well you know me, bit of a slut
" routine because she'll ask "Umm where did you meet him? You didn't speak to anyone at that bar last night." It would be different if your friend knew what you did and understood because she's the type to lie around all day and do nothing and gets that work would keep you busy. My one friend that knows the full story would be okay with me working if I went to visit his city and stayed in a hotel but I think that's so rare.
I don't think you'd be taking the piss
as such but I do think you're looking for a hell of a lot of trouble - her finding out, the hotel finding out. Worst case scenario, you've lost a friend who will feel lied to and might have a big mouth and are chucked out of your accomodation.
I get how tempting it is to work when you've nothing else to do - we make good money and men certainly keep us busy - but I don't think it's worth the risk!