Over the next three days leading up to the start of free agency, the agents for upcoming free agent players will be allowed to negotiate with other teams to see what kind of deal they can strike. They can agree in principle on all contract details but official pen to paper can't happen until March 11.
The Raiders have several free agents still unsigned who could be of interest to outside teams. Here is the full list:
WR Jacoby Ford
OT Tony Pashos
DT Vance Walker
DT Pat Sims
CB Mike Jenkins
CB Tracy Porter
DE Jason Hunter
DT Daniel Muir
If any of these players would like to return to the Raiders, they can always listen to other teams to get an idea of their market value and then give the Raiders a chance to make an offer based upon what they're told. And unless a deal has been struck in secret, that's probably just what the likes of Jared Veldheer and Lamarr Houston will do. At that point, it's the Raiders' move.
Likewise, the Raiders will be wheeling and dealing with prospective free agents from other teams during this period. They have an unprecedented amount of cap space ($66 million) with which to work so they can sign just about any player they like. They won't go all willy-nilly though so there will be much contract discussions going on over these three days.