Per the Official Site:
Tucker, 28, is expected to provide depth at several spots along the Redskins' offensive line. He has played mostly guard and center in his 5-year NFL career.
As they mention, this is a backup signing and not a solution to Derrick Dockery bailing to Buffalo for the sweet, sweet cheddar. More of a solution for the inevitable ship abandonment of backup O-Lineman Todd Wade, who could find a starting job elsewhere.