Obviously, they're immune to their own venom. I doubt there is sufficient difference between the venom of X Red and the venom of Y Red where X's immunity to his own venom wouldn't also render Y's venom generally ineffective. It's primarily a hunting tool, so I imagine it would be more geared towards prey than other Reds.
As far as other supernatural folks... It affects wizards, so the basic fact of having some form of "mojo" isn't automatic protection. All of your standard "weres" (normal were, hexen, lycanthrope, and loup) are, for all intents and purposes, normal humans when not making use of their mojo, so I would put them in the same category as wizards. Red venom would whammy them too, at least while they are in their human forms.
Whites are...tricky. They're similar to lycanthropes in the sense of being humans bound to a demon (a rage demon for lycanthropes; a hunger demon for Whites). They're not a completely different species (like Reds) or ambulatory corpses (like Blacks), and they can reproduce with normal humans. Their own powers work similar effects to Red venom, though (particularly for Whites of the Raith bent). I would call them susceptible to the venom, but maybe a bit resistant to it because they are so used to manipulating emotion themselves.
Fairies are probably a no-go. They are the entities of the Nevernever closest to mortals, but they are definitely not mortal beings. Reds feed primarily on humans. Their venom would likely be far too geared towards mortal beings to affect native beings of the Nevernever. Changelings are probably susceptible, though, being part human.
