What are the tampering rules anyway?
I think this is Cobb's agent trying to push up his client's value by leaking a rumor to the media that Oakland would love to pursue Cobb if/when he reaches free agency. It could have been an easily misinterpreted elevator conversation at the combine or it may not even have happened.
That happened to the Packers a few years back when Steven Jackson's agent leaked info that the Packers had strong interest in him - in an attempt to push Atlanta into upping its offer. Atlanta didn't bite. A few weeks later, after failing in his attempt to push the deal higher, he signed the deal with them. So it was pretty clear that the Packers interest level was "no thanks."
Can the agent be fined or penalized for tampering in these situations?
Even if there have been conversations between Reggie McKenzie and Cobb's agent, I think there's a fairly established precedent that the NFL does't even pursue those situations this close to the deadline. No sense in squashing good juice for their media partners..