It will work, but don't expect very fast call setup times. BCM 3.0 and below use H.323 V2. 3.5 and up use H.323 V4 "fast start". There was an interop patch for release 3.0/3.01 that made those systems V4 compatible.
So the answer is yes, it will probably work, but it would be a good idea to get the old 2.5 systems upgraded to something newer, at least 3.01, ideally 3.6 or 3.7 if going all the way to 4.0 isn't an option.