Hector - personally I can't see how an accusump system can be 100% effective without a check valve, certainly for pre-start pre-oiling. You need to ensure that all of the pressurised
oil from the Accusump goes to the right place.
The possibility of the valve "sticking" is fairly remote if you go for an (expensive) flap valve type of large diameter. I would use no other type.
Without going to check, I seem to recall that a non return valve is shown on the Accusump instructions.