Or, why not go for both?
The Remans could be the native species to the planet, but the Viceroy's psyhic powers could be the result of a Proto-Vulcan/Romulan ancestry - maybe a Romulan who took pity on the Remans.
I'm just saying this because I don't really think there's any suggestion that any other Remans save the Viceroy have psychic powers.
Thought that's just my impression.
Later days!
Mark
'Wish I could Help you....Wish I could tell you,
That I am real, I'm not something you invented,
That I'm not everything you want me to be.'
'And I am...Ageless. And I am....Invincible.'