Are you talking about ganking when leveling or ganking when you're 80? If someone is brave enough to jump into five level 80 druids, then I'm pretty sure they're brave enough to jump into any five man group (ok, maybe not pallys or DKs). If you're talking about being ganked when leveling, then just seeing five lower levels in one spot is going to be hard to resist regardless of the group make-up. The nice part about druids is it's a bit more difficult for them to camp you since you can stealth.