Williams isn't a perfect solution, but there aren't many of those at this point on the market. The Redskins cut O.J. Atogwe and lost LaRon Landry to free agency, so they're working to replace both of last year's starting safeties. They signed Brandon Meriweather and cornerback Cedric Griffin, who could be used at safety, but neither of those players fits the "center fielder" mold that would solidify the back end of their pass defense.
The Redskins like DeJon Gomes, whom they drafted last year, and hope he can develop into such a player. But in case he isn't ready to fill that role this year, expect the Redskins to look into stopgap veteran solutions such as Williams.
The Redskins will be unable to address the safety position early in the draft, as they're using their first-round pick on a quarterback and traded their second-round pick as part of the deal that got them their first-round pick and they also must find offensive line help. So they'll hope for Gomes to come along quickly and to patch the holes in the meantime with veteran free agents.