Check out this blog post by Michael Abrash, Oculus' chief scientist, that was posted a few days ago: https://www.oculus.com/blog/inventing-the-future/

It's clear that Oculus are spending a lot of money on research, and have recruited a lot of people. A key quote from the article is:

"I signed up to build a 30-50 person research team. Oops. Orders of magnitude matter."

So there's at least a few hundred people just in the research team, and probably a lot others in regular product engineering as well. I think it's clear Facebook are pouring a lot of money into Oculus.