Have you taken your son to the doctor for the vomiting? He could suffer from an allergy or an infection that needs to be addressed, regardless of the beer. Children 2 and under can easily suffer from dehydration from vomiting. You should talk to your doctor about his alcohol consumption and the effects it could be having on him as well, him asking for some and the tantrums he has when denied. You don't say how often or how much your child is drinking, though I don't think an occasional sip is going to permanently damage him or turn him into an alcoholic. Of course when I say occasionally, I mean just that. Talk to your pedi about it and get his opinion.
As for your husband, it's a little more complicated. The struggle for who is the dominate parent can be a nasty one, a tug of war of wills. Sadly, it's the children that suffer the most from it. You guys need to sit down and discuss your parenting agenda to avoid more power struggles like these. I would not give my children sips of beer, though that is something my husband would not mind. But I'm the dominant parent so he honors my wishes to avoid sending conflicting messages to the kids (and a good ass kicking if he just doesn't do what I say). I know how hard it is to control what the other parent does, even when you are married, but the reality of it is this is something that can drive a huge wedge into your relationship, and affect your child's emotional well being if it isn't worked out. Unfortunately, if your husband refuses to compromise or even listen to your opinions about how you child should be raised - you can either leave him or learn to accept it.
Hope you get this worked out. If you're really pissed at him you can always call CPA to report him contributing alcohol to a minor - but that is extreme, even for me.