Other than the Hackmons formats.
Absolutely definitely no. Hackmons and Custom Games are the only format where a Pokémon can have non-obtainable moves, so it's basically stuck to Splash, Cosmic Power and Teleport.
It would seem like a good pivot with its giant defenses and access to Teleport, but it is hurt by all forms on entry hazards.
What do you mean by Pivot? A pivot must have some kind of good effect from switching such as RegenVest Pivot, which is the most common pivoting way in Hackmons. Or, it could be something like passing Wish or curing allies through Heal Bell, etc.
It is also weak to U-turn and its reliance on Eviolite means it can't get rid of its hazard issues.
Not only that, holding Eviolite means it can't heal itself. So, all it gotta do is PP Stall but when it sees Taunt it is gonna Struggle. It gets easily beaten up by status as well.
Is Cosmoem at least slightly usable in any format?
If it was the slightest it would have at least a analysis, or even less a move-set submitted for it in Hackmons.
Tl;dr since it can't do anything outside of Cosmic Power Stall along with recovery, it is nigh useless and unviable in any format, except Hackmons or what X told:
It would be good in a custom format where the only Pokemon you can use is Cosmoem.
commented 1 minute ago by Giga~Blade X
That's your answer. The only way to slightly use it is in Custom matches because they don't follow any ruleset where you can have illegal moves. And, possibly only where you can have Cosmoem as the allowed Pokemon.
Hope this helps