Can you just pay to go? If so, how much?
Like Mike said, you need to be invited. And few of the people who attend are brewers. They're mainly reps, distributors, bartenders, etc.
We stopped by the brewery in early 2009. A group from Philly was there. Distrubutors and such. Owner of a well known bar and cafe. A couple of beer writters. No brewers or home brewers that I could tell. They were having fun.
One special beer camp was for the regulars at the Taproom, who had been supporting the brewery for a long time. So one could move to Chico and drink beer at the Taproom for 10+ years to go to beer camp. Not a bad idea!