I think it is a good idea, only if it is part of a larger program. For beginners, the .22 would be a good start. If someone has never run through the kill house before, how could you argue that they would not benefit from 30 rotations, as opposed to 10. (much much better than running through with blanks....hell, they were probably slanted towards using BBs, and at the last minute chose the .22s as a compromise). Anyway, CQB is not about marksmanship anyway (especially military). Moving through as a team is totally different than moving through as an individual.
After your team techniques become seamless and flawless, the you graduate to your regular load. Most units will not have the budget to run you through, using your regular load, on a consistant basis (unless you are a tier 2 kind of guy).
(.45s...9mm.....22, pretty soon it's gonna be rocks!)