Words in Scrabble dictionaries are unaccented, like the tiles. That is, all virtual ones I use are so; I've not seen a real, paper one.
Yahoo must be lying about dictionary.com (I can't find any official mention of it, mind?), or else including all foreign words in its game — have you tried playing something completely outré that also appears in Kernerman's?
Sarra, I suspect you mean that aîné is a Gastwort, if not a Gastarbeiter (at least I've never seen it do much work around here), or has the diacritic-free aine also taken up residence in English, like some freeloader in a Chekhov play? Perhaps as a euphemism to companion derrière?
But that still does not explain why it is not in the Literati arbitrator, Dictionary.com, which lists other borrowings; hence, my exasperation.
I have no idea why Literati accepted this word. Dictionary.com, which is supposed to be the word-arbitrator for Literati, lists it only as a foreign word (in Finnish and French) via the Kernerman English Multilingual Dictionary.