No... He had the time from being told that Roy would get to enter to think about it. Before then he probably assumed the oath worked as a simple binary control: either Xykon was vanquished and the blood oath wouldn't be a problem, or he wasn't and he wouldn't get in. And since he describes after-life as an oath spirit as nothing but watching the living or hooking up with other oath-spirits I doubt he had many interactions that would tip off that it wasn't a binary control.