My aunt & uncle were alcoholics. They were fun, lovely people to be around -- except when they were drinking. I have tons of great memories going fishing, hiking, being out on their boat with them. I also have somewhat disturbing memories of them at other times when they were drunk. My mom pretty early on decided that us kids were not allowed to be around aunt & uncle when they were drinking. I found that to be a good compromise: We got to spend time with some lovely relatives when they were lovely, and we got to avoid them when they turned into Mr & Mrs Hyde.
I know different families have different ways of interacting, but in my family, I don't think either my husband or I would feel that it was OK to "force" the other person into a situation they felt uncomfortable with. Like having an alcoholic family member stay with us. We would probably come up with a solution like renting them a hotel room close by.
As for having an active alcoholic babysit? That would be a total no-no for me. Like I said on another post yesterday -- would you leave your child in daycare if you knew there was a good chance the daycare provider would be drunk by the time you pick your child up? Of course you wouldn't. As codependents, we accept behavior from family members that we would NEVER accept from a stranger.
Protecting your daughter must come first. I would stay home from the wedding if I couldn't come up with a better solution than having an alcoholic watch her. (I kind of think it's odd to have a wedding with no children allowed, too, but that's just me...)