I get that people don't usually expect to play against WW top, and he has his low health gimmick, but do those things alone make him cheesy?

I would define a cheese pick as something that requires your opponent to not understand how your pick works for it to be effective. While that's definitely not uncommon for this pick, I don't think it's necessary. Secheppo has been picking him top for over half a decade in Challenger on what's often considered to be the best server. More and more WW top onetricks have been reaching high elo in their respect servers.

If even Korean pros are getting beaten by it ~50% of the time, is it still cheese?

The reason I'm making this post is kinda petty I'll admit-- a Renekton I played against called my pick cheese. I thought it seemed like the pot calling the kettle black, as Renek is a lane counter/bully that becomes one of the most useless champs once first towers fall. At least Warwick has fantastic damage reduction, aoe cc, decent dps and isn't just a slightly tanky stun-bot.