Yes, in a broad sense. The fact he's not in SAG doesn't make presenters, actors, improv performers, hosts, stand-up comics any less all the same cloth—any more than the existence of non-union actors.
I'm calling it a dick move to not show solidarity, not a violation of a specific union contract.
Mayim Bialik chose not to present questions while the question writers were striking and Ken Jennings could have done so too.
I judge him for that choice.