Well, people don't camp those rare baddy spawns because in the time it takes to wait for one of those to spawn, you could've earned the 100 gralats (and then some) by doing literally anything else. They are extremely rare, not infrequent or fairly often spawns as suggested for these pyrats.
However, I suppose the "Pyrat Leader" would probably be okay, since it mainly drops a ton of gralats and patches, which would be useless for people who have already completed the quest, so no use waiting around for it.
BUT, the Pyrat Captain sounds a lot like the giant blob, dropping exclusive items. Don't tell me people have never swarmed and lagged Swamptown for the giant blob. Only reason they stopped is because they started to get warped and most importantly because blob was broken for a while (dying in less than 5 seconds)