As the proprietor of www.GayRites.NET, a website devoted to advice and resources about gay weddings and commitment ceremonies, my first reaction to your question was similar to that 70’s gay pride exclamation, “How dare you presume I’m heterosexual!”  Your question presumes that gay couples will simply adopt all of the customs and traditions of heterosexual couplings and, thought I, how limiting is that?  One of the few benefits of the lack of social structures, support, customs and rituals surrounding gay weddings is that we get to invent our own.  Who says we need or want bachelor parties?  How … how … last century.
Then I asked my husband of 22 years and he replied, “They should each have separate bachelor parties.” So off the high horse I come. I sought expert advice from Steven Petrow, proprietor of www.GayManners.com and author of the upcoming (June 11, 2011) “Complete Gay & Lesbian Manners: The Definitive Guide to LGBT Life.”  (You can pre-order it here: http://amzn.to/eFCp5R.)  I have a preview copy from the publisher but, alas, in nearly 400 pages, I couldn’t find a word on the subject.  I had the same result with his website, though I did learn that emailed invitations to bachelor parties are acceptable.
So here’s my answer: it depends.  Make up your own rules.  What’s appropriate to your relationship?  The idea of a bachelor party, as far as I can tell, is for the to-be-weds to experience one last moment of debauched “freedom,” in anticipation of the bonds (translation: chains and limitations) of marriage.  Are you anticipating a partnership of chains and limitations?  Do you need some extra titillation andcraziness or are you just fine in that department, thank you very much.  So much depends on the couple: what if you’ve been together for some or many years and have an open relationship already?  What if you have a history of enjoying strip clubs and the occasional lap dance together? What if you’re tee-totalling, church-going, deity-fearing … errr … conservatives? Wouldn’t a bachelor party be moot?
What if you don’t buy-in to the idea that bachelor parties are supposed to be a last fling?  What if you just want to have a party with your friends or his friends or both of your friends or your families of birth or choice?  What if you can’t afford a bachelor party?  One of the great pleasures and opportunities of being part of the LGBT community on the cusp of our full civil rights (and rites) is the great freedom and opportunity to write the new rules.  So get out a blank sheet of paper and start writing.