As I mentioned, this is not my area of expertise.
Making your toys compatible with intiface central is the key.
I assume that if a game support vibrator toys connected via intiface central, the game itself might not need more than that. Toy → buttplug → Intiface Central → Game/App are separated by abstraction layers so that the Game/App don’t need to integrate with toys specifically. It just needs to make sense. Vibrator, estim, strokers etc. are different kind of toys after all. Games that support vibrators might even work out of the box with yours.
Yes but they aren’t supported by buttplug today. Publishing your protocol on bluetooth is a first step on getting them supported. Too often protocols need to be reverse engineered.
Edit:
Reading the FAQ on Intiface® Central | Intiface® might give more answers.