Is volcano bay considered a separate park needing a park specific pass?

Yes, it's one of the 3 theme parks and requires a separate pass or you can purchase a pass covering all of the parks - more economical this way. Quick tip - once in the park, head towards the far side of the volcano. There are plenty of seats there. Also, do the tapu tapu. It's a wearable device that keeps track of the virtual line. Enjoy.

I agree with Andrew's comments

It's a water park ,so yes

Yes, it's a water park

Yes, but you can get a park to park pass allowing you to go to any of the parks on the same day

Yes