Well, this has indeed been posted a kazillion times before, but of course not your fault, so don't worry. Now, there really isn't any merit at all to Rinoa being Ultimecia. That Plot Analysis you read is quite frankly awful in its section on Ultimecia and alternate universes etc. Several blatant mistakes and bad arguments and so on. For a much more detailed and comprehensive breakdown of R=U read the R=U section in the "Time/Ultimecia Plot FAQ" found here:

http://www.gamefaqs.com/console/psx/game/197343.html

ie. where the other FAQ you read is.

Now, I know I co-authored the FAQ, so it probably sounds like I'm blowing my own horn or whatever, but I'm quite confident that it gives a more logical approach to the whole issue.

Now, as for Ellone being Ultimecia, that is definitely not plausible either, I'm afraid. There's nothing that indicates it, and Ellone isn't even a sorceress...

EDIT: If you want the simple explanation as to why R=U has no merit by the way, the Marginally Official FF8 FAQ thread summarises the basic argument from the FAQ as such:

The FFVIII Ultimania guidebook is an official publication containing detailed background information on Final Fantasy VIII. According to this guide, the sorceresses in FFVIII have normal human lifespans. As Ultimecia lives "many generations in the future", it is highly unlikely (since this is a game that involves magic, after all) that she and Rinoa are the same individual.