The answer should be, at least one of them - Samari Rolle.
The Dolphins have already signed former Arizona Cardinals CB, Eric Green this off-season and I'm not sure how much depth they would like to add to the CB position. McAlister would be a decent veteran corner to add, but I'm not sure if he will start or warm the bench.
As for Samari Rolle, here's a guy that the Dolphins should consider as a solid back up safety to Yeremiah Bell and Gibril Wilson. I believe that his addition can definitely make the case for a solidified Dolphins secondary - something we haven't seen since the Patrick Surtain and Sam Madison era.
Both Rolle and McAlister are in their early 30's and probably won't be long term solutions for any NFL team out there today. At any rate, I'm sure many teams will consider adding a veteran piece to their secondary unit if they are lacking depth. The Miami Dolphins definitely fit the profile of a team in need for some extra back-up, especially with the bad luck they've had with injuries at the CB/DB positions. Last season was an exception to the rules because the Fins actually had some continuity in the secondary, which could have been part of the reason why they were so successful.
Samari Rolle has played 12 season in the NFL and has recorded 431 total tackles (solo & assists), 123 pass deflections, and 31 interceptions. Chris McAlister has played 11 season in the NFL and has recorded 339 total tackles, 89 pass deflections, and 26 interceptions.
Each player has solid statistics that show a consistent performance throughout their long careers in the NFL. THey were both a big part of the Ravens well-known defensive dominance, particularly McAlister (who was a part of the 2001 Ravens championship run).
I would be satisfied with any of these two guys wearing a Dolphins uniform, but I would believe that Rolle would be the more sensible addition. We'll see what Bill Parcells decides to do with his talent evaluation instincts. Stay tuned for an MSG Fin Meter evaluation in the case that either of these players join the Dolphins in the off-season.