I also might be able to explain why flood infected hunters are never seen in Halo. It is pretty much obvious that Fuel rod cannons are extremely unstable (The ones that Grunts drop explode with the same destructive power as a plasma grenade). Maybe the Hunters have some sort of natural, organic mechanism inside their body that keeps their Fuel rod gun stable, that hangs on even after death. What happens when the flood infect, though, may inadvertently bring about the death of themselves. Flood pretty much ignore all stimuli from their hosts (This is why sniper rifles don't work on them and they keep getting back up after being shot) Maybe when the flood infect the hunter, they disable that organic mechanism/ gland/ appendage/ whatever that keeps the fuel rod gun stable and ignore the stimuli from the host that say, "Hey, dumbass, that thing in my arm's gonna explode!" The cannon would quickly destabilize and explode, killing the flood, the flood's host, and any nea! rby flood. Once the flood are dead, they cannot adapt to something, so they'd never figure out that infecting a hunter results in a big boom.
It would sure be fun to see, though. :-)