I just read the transcripts for that Skip's scene in Inside Out(season 4 is not a favorite, I think I've only seen that scene once).
In that scene, Skip was just pretending, trying to not tip Angel off that he was on team Jasmine. For all we know, Cordelia was just put in a holding cell for when she could be returned to earth, as Jasmine's puppet. I bet the Buffy reference was just thrown in because skip thought Angel might know about that, and it was needed to the lie.
Even if there was just one heaven, I doubt Cordelia was in it. Jasmine would probably have more control of a seperate space. It could be that she had power enough to hold Cordelia in Buffy's Heaven, but that doesn't seem likely, and it seems risky.
But I assume there's several Heavenly dimensions. I mean, people keep saying there's several hells, so I guess, depending on your definition, there's several heavens. If someone from Connor's Hell dimension, whatever it was called, came to Earth, they would consider this paradise. Although, the fact that Skip only referes to the one Paradise, implies that he atleast think there's only one. Or that he thinks Angel thinks that. Or he was just being generic, meaning that Paradise is the term for all heavens. But even if Cordy was kept in a "real" Heaven, what are the odds they're in the same?
This is of course assuming that Skip and Jasmine "ascended" Cordelia on their own, as he says(she said she worked for them in season 5, didn't she?) Maybe TPTB did want to ascend Cordy, put her in Heaven, and it was Skip and Jasmine that got her out of there. Even then, Buffy died so she was simply dead, while Cordelia supposedly had work to do? I can't recall the last ep of season 3 that well. I mean, their stays where so different. Either way, doesn't sound like the same place. Or maybe it was the same Heaven but Buffy was in sleep-mood? Or she forgot everything when she got back, but Cordy didn't?
To sum up; No, I don't think it was the same universe/dimension(Or maybe it was, it's not like they had the room next to each others, if you know what I'm saying). But maybe there is only one heaven and Skip pretended that's where Cordelia had been. But then again, what about that axe thingy Angel used to find Cordelia? Jasmine had to make the plane Cordy was in to seem to be a higher plane, for her plan to work.
I have no idea. It is possible that this post will confuse you more than help you figuring this out.