The Nike Campus isn't open to the public, but the Steve Prefontaine building houses a little museum of the Nike Archives that may or may not be open depending on the day. If you're not acting suspicious you can walk around and nobody will bother you. However, if you're wearing Adidas or something other than Nike shoes, prepare to be noticed/bothered by people. I heard someone call security on kids running the berm trail in non-Nike shoes a few months back.
Generally, while security does patrol the running trails to make sure they're safe, they're not looking to kick you off. In regards to the track, availability completely depends on if the track is being used. Some days it's fine, other days you'll see signs asking you not to use the track. It's a damn fine track though.