Yup -- in fact, it's better for Dumervil that way because he gets an advance in salary of $5 million. The reporting on this is crazy. It's not some massive screw up. It's a guy with a big cap hit getting cut. If he was willing to take less than his contract to sign with Denver, they can still do it and not have to increase the cap hit over what it would have been with the salary reduction, simply by (as you say) making the payment in the form of money that can be spread over the three years.
If the agent was trying to play a game by getting the Broncos to miss the 4 p.m. deadline, or if the Broncos even think that's a possibility though, I can't see them wanting to go near the guy. That is about the most slimy thing imaginable.