A:AnswerI wouldn't recommend it. The Oculus webpage is pretty specific about how beefy the computer has to be in order to run VR. And I'm sure it would run on the Omen, but would probably be pretty laggy.
A:AnswerIt is replaceable, but it's not as simple as popping it out and putting in a new one. You have to get inside the casing to get to the battery. I found a guide on hp's sire that has a video to follow along with.
http://support.hp.com/us-en/document/c04506712