I have poured, along with other HBC members, at a commercial beer festival in our town in CA. I checked with the organizer who checked with the ABC. I was told that it was allowed....at least in CA. Now I don't know all the specifics but it seems like it met the letter of the law
1. The homebrewers received no form of compensation, it was all done by wristband so there were not even drink tickets to collect.
2. All proceeds collected went to a 501c non-profit
3. All pours were in a 3 oz. sample glass
4. Now this is the big one IMO....it also involved two beer competitions. One was a straight out Best Beer contest and the other was a People's Choice contest. It looks like according to CA state law that homebrew may be served in a festival type setting along as it is part of a competition, tasting, or judging. http://www.homebrewersassociation.org/pages/government-affairs/statutes/california
It does not stipulate who can be a judge or how many judges the competition can have.