I wouldn't call it a conspiracy theory. In fact, it's an easily plausible scenario. However, I would think that Rodney as a free agent would land a million+ dollar signing bonus on a two-year deal and therefore not need to worry about getting cut. However, I can't claim to have the pulse on the 2008 free agency market.
First off, a million dollar signing bonus on a two year deal doesn't protect you from getting cut because your dead cap is $500K. Darius current dead cap is $600K in 2007 and none thereafter. Rodney's dead cap is $732K this year and next. What protects a veteran player with little dead cap from being cut is a combination of performance and willingness to adjust his salary to be in line with his value.
As for what Rodney could get on the open market, here's an update from PFT with the details on Darius contract. He got no signing bonus, $600K guaranteed of his $1.6M salary for 2007 (yup, that's $400-600K LESS than old Rodney is still getting on his recently tweeked deal) and with straight salary and no roster/option bonuses on his remaining 2008-2009 salaries Darius can be asked to restructure (take a pay cut) or be as sat on through camp and cut in August of any 2008 or 2009. He didn't get the deal he wanted, he took the only deal available. So I guess that tells us something about the market for 30++ safeties coming off back to back injury plagued seasons.
http://www.profootballtalk.com/rumormill.htm
DARIUS DEAL HAS LOW RISK FOR RAIDERS
A league source tells us that the contract given by the Raiders to safety Donovin Darius includes a signing bonus of (drum roll, please) nothing. Zero dollars, zero cents.
But the deal contains $600,000 in guaranteed base salary for 2007, which means that Darius has some protection against getting cut -- and the team has some protection in the event that it needs to cut him, since a decision that Darius no longer has it means that the team will have spent (wasted) only $600,000.
Also, the absence of a signing bonus means that there will be no cap consequences in 2008 or 2009 if the team decides to move on. (Sorry, but we're not in the mood tonight.)
In all, the deal has base salaries of $1.6 million in 2007, $2.5 million in 2008, and $3 million in 2009. And the fact that the 2007 and 2008 compensation is entirely in the form of base salary means that the team can squat on Darius until the eve of the regular season, and drop him with no consequence.
The better approach for Darius would have been for $1 million of the base salaries in 2008 and 2009 to have been pushed into roster bonuses, due on the first day of each league year. This would have forced the Raiders to make a quick decision each year as to his status. And if the decision would be to move on (still not in the mood), Darius would have had plenty of time to land elsewhere.
Then again, the deal Darius signed simply might be the best one he could get, and that the Raiders refused to move any of the base salaries in 2008 or 2009 into roster bonuses. It's not as if any other team was beating down the door to sign him.