Yes, the heaters can be fed from a separate panel, so long as they're all fed from the same service. It's common to feed lighting and heating from separate panels- half the time, they're at different voltages anyhow.
If there is the intention to plug medical equipment into the receptacle outlets in these rooms, then I would not risk putting the heaters on the generator circuit if there is a potential to overload. It's more than an inconvenience, it's potentially lives at stake.
