The venom is injected using the dorsal spines. They are not poisonous so they can't wipe out a tank. They might be able to kill a fish but probably not. Most fish don't fight with Rabbitfish except other Rabbitfish.
Foxface are the nicest fish you can add to your tank. I feed mine with my fingers it is so cool. Just make sure you feed it correctly so the color doesn't fade.
I have mine with a blue hippo and no problems. It does fade sometimes, but only temporarily. I believe it has to do with it's mood. Mine did go after my entire zoa collection and one of my frogspawns.
Mine goes camo when he goes to the left side of the aquarium. On the right side near the rocks he stays bright, if he enters the left he goes full camo mode, almost always. He looks like a zombie when he does it.