I remember hearing something about ocato being an aylied.

Is there any truth in this?

By the way could you please link me to the thread where it was discussed?

Well you'd have to ask the people who made that argument. I can't think of anything that suggests he is.

neither can I. But I thought it was just my lore ignorance.

I'm pretty sure he's not, given I remember him being specifically from First Hold, was he not?

http://www.gamesas.com/bgsforums/index.php?showtopic=790274&hl=
That topic has it covered.