Well, the Ultimania Omega does go over it in the story summary, so that's for real too.
Ultimania is sadly not perfect
I agree it's not a big deal since it's just a game mod, but I have to wonder why you'd want to make Reeve not be part of the team.
There is no way to place him in it. At one point you are talking to the character at the exact same time as reeve is talking to Scarlet. It isn't feasible to make a stupid story element to make it work, plus I think reeve serves his purpose as part of Shin-Ra, even if he doesn't like it.
Out of curiosity, what are you going to do with him at the Temple of the Ancients?
This is the one thing that causes an issue with decent story telling. To be fair is was pathetic in the original that new cait would just pop up that fast...not only that, but he has to solve the puzzle. The constraint isnt in the story but in the fact we are forced to accept that he has to be in the temple at the time. No way will work with this to make it a plausible tale, so instead I will have to accept the explanation I give it as "one of those things"
personally, I think having some established person or party member die at this point would have been cool.
A human who says, does, and acts how Reeve wants him to?
No, I have made him work for shin-ra and reeve, but along the way he begins to understand that there is more going on and that he has been working for the wrong people. His character adapts so that he ends up helping cloud.
He has his own personality....the core of the text as you know it will be altered to fit in with that story. The whole cait sith storyline aside from a few things will be changed.