Its easy to say "its a party...noone will care". But I totally understand. Our wedding was like that. My husband's profession, which is heavy on the traditional politically conservative side, clashes with my profession which is heavy on the liberal side (let's just say big oil company vs media). Then we threw in people with old money, people with new money, people with no money, highly educated, no education, church friends, childhood friends and family (spanning 3 overseas countries and several languages) on the invite list, along with my husband's athletic team, a few macho marines, and tossed in a few of our GLBT friends and it made for an exciting evening. I was a nervous wreck all the way leading up to the reception but looking back on it I think since everyone didn't know anyone else, they were all friendly. Near the end, they all stayed in their own little community groups anyway, so there wasn't any huge clashes of decorum or manners.
I think you have every reason to be nervous. In the end, its up to you on what you are willing to let go and accept what's out of your control (or what's in your control) in order to give your husband a wonderful bday!