Abeloth at this point is imprisoned within the Maw still, and as far as I know, there is no way to get out. What we know is that the Emperor is a man, he is old, and he is very powerful due to his Mastery of the Dark Side. That is all certain.
I can see a few holes in there though. Possessing someone doesn't change their physical appearance, which is something Abeloth does, possession I mean. That he's old just means he aged. That he is very powerful can be attributed to Abeloth.
I'd say the biggest thing is that SW has proven before they have no issue with using bits of extended universe and completely ignoring others. Example, Chiss being involved with the sith at this point in history, Rakata being involved at all, Sith purebloods existing in this time period etc etc. Bioware is infamous for taking things it likes, and ignoring others, just like LucasArts.
I'm not gonna discount the emperor being Abeloth. I wouldn't also believe anything regarding the emperor's indentity unless it's a confirmed legit Lucas Arts/Disney or Bioware resource. Not extended universe.