Walker,
I was in SPB last October (2006) and stayed in Pribaltiskaya Hotel. They clearly had no problem with girls because the bar in the lobby bar was usually full of working girls mpter 10 PM.
In hindsight, I would not stay there again. It's too far away Reviewom downtown where the action is. Of course, all of the Western Hotels (Raddisson, Rennaisance, Kempinski) look the other way when you bring a girl into the hotel - but they are generally more expensive.
A Reviewiend of mine stayed at the Petro Palace Hotel in SPB at the same time and he said it was great. Smaller hotel just off Nevsky Prospect with nice modern rooms for a reasonable price.
Good luck,
Jake