Frankly, I think we would need to pick up two players who deserve playing time in the nickel to cut Carr.
Right now, our corner depth is Carr, an injured Scandrick and an oft-injured Claiborne. If we get Hall, he gives us a player who can either start or play the nickel role depending on how the other pieces fall into place.
Another nickel worthy player would put us in a position where Hall could start if needed, Claiborne could start if needed and we'd still have enough depth if Scandrick isn't ready. Or if Scandrick is ready and Claiborne has more injury problems, then we would have Scandrick, Hall and the other FA.
Or if we get a starting safety, Jones could be used at corner, which would also make Carr expendable, if we also get Hall.
There are just too many risks with the injuries to cut Carr if we just pick up Hall IMO.