Viable Support?

yes. with the recent change to stoneborn and the courage mastery he is viable as a support. He is better with/against adc casters such as but some of the mage supports make your life hell.

No

might depend on what you mean by viable. He certainly has enough CC, and with your passive, you might even have enough sustain.

Is he competitive, compared to other options? maybe, maybe not. He's not balanced around the support role, as he's mostly played toplane, So I would call it some what unlikely. Also, he doesn't offer a unique function that makes him particularly fit for support. Alistar's ult can make him tanky without a ton of items, Braum's shield can block attacks, Kench can devourer enemies to protect them. But Maokai doesn't seem to have a lot of protection, that doesn't require some items.