Hi Doug,

It should be just fine, treat it as if it would be primed canvas. The only set back is that you would be relying on the wall beneath the primer - if it is a new construction - you are good - monitor the priming, several (3 or so) coats of oil based primer with light sanding in-between.
If you are going over old paint then you must make sure that there is no bubbles (lifting of the original paint) or water stains on the plaster within the wall, etc. etc. If there is it should be scraped, sealed, patched after the source of damage(moisture) is found and fixed. When you are satisfied with the wall condition prime the wall with (2 or so) coats.

In your case - painting sections here and there. I would paint the entire wall to the final color first and then paint the murals over.

ilia