The parties I go to, no rule about kissing, some people do, some don't. When it is your turn you do what you want, as smiths said punting and in particular parties are not for the squeamish.
Indeed this issue keeps coming up, i see a poster asked about services on another thread and mentioned STIs. If your that concerned parties arent for you is my advice. I go to the GUM quartely and fortunataly have only ever tested negative, sure that could change at my next visit.
I take the risk for the reward on offer, a punter has to assess that risk for himself of course.
A sex party is all about multiple WGs and punters sucking and fucking each other, its not a vicars tea party, i am not sure what punters expect goes on but i can tell them assuming its a good party non stop sucking and fucking with some concentrating more on RO. If any of that is a concern to a punter its quite simple, dont go.