NFP has Culliver rated as the second-ranked free safety in the draft. They rated him at a 6.4 D M which means that the player has the potential to be a starter, despite one deficient area. (Interestingly enough, the D and M ratings indicate he has no weakness in any critical factors and lacks football intelligence).
NFL.com says the following:
Culliver's a mid-round talent with higher upside. The 49ers add an intriguing talent to their secondary with the selection of Culliver. He has a good combination of size, speed and ball skills, and will push for time in their nickel packages.
Perhaps Sonoco NinerFan said it best on our forums:
Culliver was ranked as high as 76-80 by Wes Bunting and [The Webzone's Own] MadDog and 102 by NFLDraftScout (Rang). Mayock says sixth rounder and suddenly it's gospel?
Basically it's another case of "we won't know until we know."
The addition of Culliver, though, probably indicates the 49ers are not high on their current crop of safeties. Mays was a bit of a disappointment his rookie year. Even the coaching staff that drafted him benched him in favor of other options. With Goldson, Mays, Reggie Smith (seriously, what's with all the Smiths?) and Taylor the 49ers starting safeties could look different in Vic Fangio's 3-4 scheme.
After Culliver's conference call it looks like the 49ers are projecting him at CB. What was interesting was that he said the team wouldn't let him fail. He would try CB and if that didn't work he would default to safety.
Either way, it looks like Baalke has plenty of faith in the coaching staff's abilities.