So I've seen several threads where there was viable reasons for a ship type to exist on both sides of the fence. Example : Corvettes (CR-90) were not used solely by the Rebels but also were employed to a lesser degree by Imperials. With this in mind what are some other cross over/common vessels that could work both in Epic or standard x-wing games?

First thing that comes to mind is the Nebulon B Frigate

Nebulon B definitley, but really any smaller Imperial ship would also be on Rebel lists due to defection or capture.

Lots and lots and lots:

Z-95, ywing (to a small extent till phased out), YT's, Firesprays... Lots were used by empire until phased out for the tie line.