Are Watchers still canon?

Well considering that The Lost Tales of Ornn refer back to the Howling Abyss and what it's intended purpose was, yeah I'd say they're still canon.

They have been mentioned recently, but no specific or straightforward details have been given in a long while.

Watchers have always been a confusing element to the lore, and if my personal opinion had any sway I'd have them retconed or at the very least heavily reworked. Although its just their appearance that is a confusing mess. Oh and what they are exactly is too, like so far they're just more interdimension overlords.

Ornns story mentions them.

Yus