It's not Rinoa, but you're correct about The red saviour being Ragnarok!
The riddle:
Myself,
The victim of the preceptor,
Avoidance,
The dilatory assassin,
The daedal burg,
and The red saviour
Am I all? No.
Am I some? No.
Mayhaps, in clearer light
and in array
my true self will come forth,
as I am in all.
I am the beginning.
Wrong guesses:
Ultimecia
Ifrit
Cid
GeroGero
The clock puzzle in Ultimecia's castle
NORG
Lunatic Pandora
Rinoa
Ellone
Deep Sea Research Center
Eden
Gilgamesh
The moon
Hints:
The answer is not a major part of the game (i.e. main characters, time compression etc.)
The answer is not an enemy.
The second, third and fourth paragraphs all give clues about how to solve the first paragraph. The first one is possible to solve without their help, but easier with.
Try to put the first paragraph in other words.
"The red saviour" refers to Ragnarok.
The answer has little to no ties to any story or plot at all. It is involved in a process, though.
The first six lines are not a description of the answer's attributes or surroundings, but rather a list of individual "things" that can lead you to the answer. Also, think of the two following lines (Am I all? No. Am I some? No.) in connection to the previously mentioned.