I would wait until after their last round of shots, then its whatever you are comfortable with. I think it is good for a pup to get use to the sights and sounds of the game. Plus its a good opportunity to socialize as nearly everyone there will want to love on a pup. Just be aware, not all big dogs like a pup crawling all over them! Keep a lead on it.
I've done it before when I thought the pup would be better with me than with a dog sitter...but only if the pup had all it's vaccinations and over 3-4 months old. Otherwise, I keep them home.
I've seen them at hunt tests when people are trying to sell them. Someone brought some pups out to a field trial in Amarillo, Texas many years ago, and I heard from my pro later than some of that litter came down with parvo.
It really depends on the grounds. If the trial/test is at a refuge open to anyone, no way. If the grounds are privately owned, I would be inclined to take a pup. Now I probably wouldn't take an 8 week old. That is an awful lot of sight and sound stimuli for one that young, but a tad older, yes.
And what Gavin said. Pup is on a short leash at all times. Not all humans love puppies and it's completely disrespectful to let a pup get in the face of a working dog.