I don't think this story is remotely close to having legs yet as there isn't any indication that the team illegally discussed anything with Chad Johnson, but it should get noted anyways. In two posts at PFT Mike Florio accuses the Redskins of tampering in strong language. First:

Here’s our take on all of this — the Bengals should be very concerned about the possibility of tampering.  The Redskins have enjoyed over the years a very strong relationship with Drew Rosenhaus, Johnson’s agent.  And it is believed by some league observers that Chad’s campaign to be traded arose not from his zeal to wear a new uniform but from his desire to stuff more money into his pockets. 

Thus, if the Redskins were willing to make such a strong and specific offer for Johnson, it’s hard not to think that they have an idea as to the contract extension that Johnson (via Rosenhaus) would accept.

And that, of course, would be tampering.

And now:

And we continue to be (more) concerned that tampering might be occurring with Johnson.  Even if the ‘Skins aren’t directly talking to agent Drew Rosenhaus, the fact that the Washington Post knows that the team is ready to pay Johnson $21 million in guaranteed money strongly suggests that the team is putting this information out there in the hopes of continuing to stoke the “I want out” fire that has escalated into an inferno.

In our opinion, what the Redskins apparently are doing is 1000 times worse than the conduct that formed the basis for the Bears tampering allegations against the 49ers.  In our opinion, the Bengals should file tampering charges against the Redskins today, if for no reason other than to get the Redskins to back off.

I'm not that familiar with the league's tampering rules. But recall what got the 49ers in such hot water with the Bears, not too long ago:

Following a detailed investigation and a hearing, NFL commissioner Roger Goodell has determined that the San Francisco 49ers violated the league’s anti-tampering policy last season by contacting linebacker Lance Briggs’ agent without the Bears’ permission...

The Bears had filed tampering charges against the 49ers to initiate the proceeding. Briggs, whose contract expired following the 2007 season, agreed to a six-year extension with the Bears March 1, the second day of this year’s free agency period.

What that tells me is first and foremost, the Bengals have to allege tampering before the Redskins can ever be accused of it. Second, whether the Redskins did or didn't "tamper" is a factual matter totally irrespective of whether or not Mike Florio thinks "what the Redskins apparently are doing is 1000 times worse than the conduct that formed the basis for the Bears tampering allegations against the 49ers." Tampering is an NFL rule violation, not a violation of Mike Florio's Personal Moral Compass. And it will apparently depend on whether and to what extent the Redskins contacted Chad Johnson (which is, again, a factual matter totally irrespective of the wrongness or blameworthiness of what the Redskins did per Mike Florio).

I hope there was no tampering. I don't see any indication from the Bengals or any other league source that there was tampering, though reader(s) are all encouraged to keep their eyes open.