I think it would cure just fine assuming you have the hardener in the right proportions. I have brushed epoxy on some spots without issue. It may take a little longer to cure, but should be fine if you aren't impatient about cure time. The critical thing is prep before applying primer, either by brush or spray. You can also reduce it the same as if you were spraying. I've sprayed rattle can undercoating, both 3M and Upol brands over epoxy primer without issues with lifting. The primer was fully cured before applying the undercoating.
