What you're going for, I think, is identifying which teams retain the ability to offer more than a prorated share of the vet minimum to a free agent. Being subject to a hard cap doesn't mean that a team can't offer more than the minimum. It just means that their total spending can't rise above the apron. If they retain a salary cap exception and sufficient space under the apron, then they can offer more than the minimum. The three hard capped teams listed above have used their available salary cap exceptions for 2014-15 and can't offer anything other than the minimum.
Dallas and Cleveland both signed free agents using cap space and used their room exceptions, so both of those teams also are down to minimum offers.
There are other playoff teams, however, that retain salary exceptions or cap space. Atlanta, for example, has almost 5M in cap space remaining (Danny Ferry would be the frontrunner for Exec of the Year in a normal year).
Basketball Insiders has a one page summary that shows all remaining exceptions and cap space:
http://www.basketballinsiders.com/nb...s-at-a-glance/
Lack of an available roster space is no real obstacle to signing a free agent at this point as the least valuable player on the roster can simply be waived.