I'm not sure about the improved versions, but the standard Heavy Medium and Heavy Small lasers can be used on BA. The problem for the HML is that it's a full 1,000kg, so there's not many BA than can carry that (I think only Assault BA have enough space)
Sure. Just, TacOps, where the improved versions are found, neither lists "BA" among the units they're available to (which it does for ER pulses and VSPLs) nor has BA equipment stats for them in the relevant table. So, looks like specifically those can't be put onto battle armor unless some development or other I'm unaware of has changed that since.
That's enough of a sidetrack though, I think. This thread is still about the Roc -- whose HML version could indeed be pretty painlessly be upgraded to the improved model. :) (Well...possibly modulo the explosive nature of the new laser. Come to think of it, I don't know for sure if and how Protos
do handle an explosive weapon being hit...)