So, if the character wants to join a given Covenant and/or Court, and convinces the members to be accepted, I see no reason for this not to work. Actually, in my chronicles it isn't even too rare to have a member to one organization that isn't at all a member of the usual splat. It runs completely on shared interests.
That said, the ST should analyze and work any mechanical benefit of the membership actually tied to the splat at an individual level. It is impossible to address every possibility.
That said, lets construct. Maybe in the Vampire-Geist, we could use the Draugr as a starting point? It is death to the Humanitas in the Kindred. What if a Geist, taking the leave of the last remnants of a human soul from the undead body as a true death, strikes the Bargain with said soul, giving it another take in the fight against the Beast? The result is a second chance, but not the kind the Geist expected to create, once it finds out it will not be the only thing influencing the host.
Now, how could the Embrace spoil the Awakening, or the Awakening affect the Cursed? The first and most obvious, an Embrace on a mortal in the verge of Awakening, or even during the process of Awakening. On the Legacy take, I do not think of a Legacy that turns a Mage into a Vampire. But what about a Mage teaching a Legacy to a Vampire? What about a Vampire that braves through a incursion of the Abyss and find the way to a Supernal Realm? Maybe the Kindred, being what they are, can brace themselves against the Abyss in a way no Mage can, and find the secret and most direct ways. But how would the Curse corrupt the Supernal?
Elfive appointed one thing we need to keep in mind, at every instant here: this is tentative and cautious so we never, ever, doesn't matter what happens, never give again raise to the Height...