Most Japanese folks who frequent Western themed bars (rock bars, reggae bars, the Hard Rock cafe as Zaff mentioned) are open to the prospect of being approached by and chatted to by a foreigner. TGIFridays, the American eatery, is also full of Japanese and foreign folks and I saw plenty of people getting along whenever I'd eat there.
As for finding a good place for service, you'll find that unless you speak Japanese well enough to carry on a conversation with the gentlemen working in the front office who arrange said activities, you'll be turned away. They'd rather lose your business than deal with a gaijin who can't speak Japanese and doesn't comprehend the system. It's more of a liability for them than a sales opportunity.
My cousin brought me to a hostess lounge one night and we had trouble getting in because of my presence, despite the fact that he was 100% Japanese. (I'm half, and a strongly dilluted looking half at that). We eventually got in but, would have been no dice if I'd been on my own.