I just occured to me that now, snice you make an ally of a spirit you summon and bind, possession traditions such as voodouns can summon an ally spirit and channel it. Not really that different than what they've been doing before, except now there's real rules for being a mounted voodonu and acutally being able to control yourself. Plus, since you can do it w/ an ally, you have more control over what powers are available to you. And there isn't massive amounts of drain associated with it. What other traditions does this work with?

None? Only Possession traditions get possessing Allies and Channeling.

All of the possession based ones, I'd think.

There are other possession traditions than Voodoo but, as Rotbart mention, non-possession traditions don't have the option of possessing allies.

The Quabalistic (sp?) tradition is a posession-based tradition. I think there's a couple of others, but I don't have my book with me.