What I've read seems to suggest "no". I haven't found anything in the SCAG that suggests this as true.
I'm aware that in Adventurer's league there was a reference guide for the monsters in Volo's for playing them at the table, but I can't find it.
And of course I'm ignoring the "be what you want to be" rule. Because I feel that if you are playing in a campaign setting such as Forgotten Realms you need to apply the rules of that realm, and as far as I can tell, it rules that Yuan-Ti are evil snakes.
I know that as Yuan-Ti are regarded as evil, one might apply similar logic to the Drow, but even in the Sword Coast Adventurer's Guide it mentions that heroic Drow such as Drizzt have changed the minds of people. But nowhere in the book did I find a similar entry about Yuan-Ti.
So to the extended knowledge base here, are there examples in the novels, sourcebooks, etc, that would suggest Yuan-Ti are good?