There is only one thing I am worried about with Culver, and that is his range. His range when he plays centerfielder is not the best, but not bad by any means. Can he float middle and get to the sidelines in time?
The fast guys can't do that either unless they anticipate the pass first
Let's take a look at some free safeties.
Jets: Kerry Rhodes - 4.56
Bills: Jairus Byrd - 4.68
Patriots: Brandon Meriweather - 4.47
Dolphins: Gibril Wilson - 4.47
Ravens: Ed Reed - 4.57
Bengals: Chris Crocker - 4.55
Browns: Brodney Pool - 4.52
Steelers: Ryan Clark - 4.48
Texans: Eugene Wilson / Dominique Barber - 4.48 / 4.68
Colts: Antoine Bethea - 4.39
Jaguars: Reggie Nelson - 4.48
Titans: Michael Griffen - 4.45
Broncos: Renaldo Hill - 4.68
Chiefs: Jarrad Page - 4.63
Raiders: Michael Huff - 4.34
Chargers: Eric Weddle - 4.48
Cowboys: Ken Hamlin - 4.61
Giants: Aaron Rouse / CC Brown - 4.58 / 4.52
Eagles: Sean Jones / Macho Harris - 4.63 / 4.68
Redskins: LaRon Landry - 4.35
Bears: Danieal Manning / Kevin Payne - 4.48 / 4.60
Lions: Louis Delmas - 4.52
Packers: Nick Collins - 4.36
Vikings: Madieu Williams - 4.48
Falcons: Thomas DeCoud - 4.50
Panthers: Charles Godfrey - 4.43
Saints: Darren Sharper - Unknown but certainly in the 4.6 range at this age
Buccaneers: Tanard Jackson - 4.52
Cardinals: Antrel Rolle - 4.48
49ers: Dashon Goldson - 4.60
Seahawks: Jordan Babineaux - Unknown
Rams: O.J. Atogwe - 4.52
The average there is 4.52, and Tyrone Culver is a 4.62. His presence would have given the Dolphins the 5th slowest Free Safety position in the league last year. But, how much does that matter? The defenses with equivalent speed free safeties (guys that ran worse than 4.58 in the 40 yard dash) include the Saints, 49ers, Cowboys, Bills, Eagles and Broncos. The only defense that was really bad and also had a slow free safety was the Chiefs.
What it suggests to me is that it wouldn't be a huge problem. Plenty of those names at free safety have great speed but are bigger liabilities overall.