Epoxy vs Vinylester

[McReef]

My impression was that you can can poly on top of poly, or epoxy on top of poly, but you cannot add poly on top of epoxy (no chemical bond).

I think you are on track there. From what I can gather, while epoxy will cure just fine over poly (and bond aggressively), the chemical makeup of epoxy actually inhibits the curing process of poly and vinyl resins. The lack of bond is due to the fact that the newly applied poly/vinyl resin never fully and properly cures at the interface of the two materials.