I also agree with ewest that if hybrid BG are your primary focus, then it's easier to manage them independantly in their own pond. I really think if a person wants hybrid bluegill then they can definitely make them work, it's just that you raise the difficulty factor of overall management exponentially with every species added. It can be done, but the system will be less predictable.
By the way, I will bet any amount of money, that if placed in a well managed pond, with ample numbers of prey items, all other things being equal, a purebred bluegill will outperform a hybrid bluegill in ultimate size, assuming we're talking about bluegill/green sunfish hybrids. I know that my bias is showing through, so I'll just come out and say it...I love purebred bluegills. Most studies report (and if you scan state by state angling records) that the purebred bluegill has a better top end than BG/GS hybrids. Think about it. Why would a fish that grows to two pounds, mixed with a fish that grows to one pound, produce a fish that grows to three pounds?
The reason, once again IMO, that hybrids sometimes grow faster is because of their agressiveness and larger mouth parts allow them to utilize prey items that bluegill can't at an early age. YOY and age-1 hybrids will often compete directly with your largemouth bass population for larval and fry size fish, giving them an early boost. If your pond is in good balance and producing a great crop of zooplankton, then that's when the purebred bluegill really shines!
Remember though, it's all up to you. Gather information, get the checkbook out and pull the trigger. It's all a great game with no set rules and no absolutes as to the results. Others may disagree with me and prove to be right in the end. You just never know.
Too much fun!
