She had taken up the title of Darth Traya, but that might have been, more than anything, her choice to do so and not reflective how she really felt. We all know that she was Dark Side. At least, what she planned to do would be Dark Side. I think she had fallen to the Dark Side, but didn't consider herself Sith. She considered herself above the Sith, in a way, for she was using them to accomplish her ultimate goal
Dark Side definitely, but by definition - not Sith, Jedi or any group of Forces users. After all, dark side and light side you don't have much choice him. But the rest are just sects, groups, philosophies - If you deny being in one you categorically can't be in one. Kreia was set apart, in her hatred of the Force she developed a new philosophy - unfortunately she didn't have many followers... :P
Arren Kae? I don't know. Kae was a Jedi that fought in the Mandalorian Wars with Revan. Her and Kreia have similarities in their backstory. The similarities are definitely there, but, if we are referring to them being the same person, I can't comment or speculate. There is one glaring flaw in this comparison: Kae fought in the War, but Kreia did not (so she says
). For now though, we can say that they were both Jedi Historians and were both exiled for teaching Revan.
In my head canon, she is Arren Kae.
Everything slots into place, even that part about the war. After all Master Kavar said 'I thought you'd died in the Mandalorian Wars!
" To which she replies "Die? No. Grew stronger. Yes." Heavily suggesting she did participate.
Personally I think Kreia is not her real name, but an alias in which she hid from the Jedi and perhaps the Sith - if they knew her true identity as Arren Kae AKA Darth Traya - they would kill her on sight. But hey, thats just my opinion.