It should be whatever Wakko prefers. Perfectly fine for a nonbinary person to use "he".
Edit: And also, pretty sure that's another layer to the joke. Cause Wakko is just out there living his life while the world spins around him making definitions and boxes that have no bearing on how he lives.
And sitting in a place of extreme privilege I say, meh, be you. Look everywhere. Here, there, wherever. If you catch someone's eyes share a quick smile and look somewhere else. Fuck'm
First, be you.
Second, try to remember no one cares, and if they do, that's on them.
Third, ok, so don't stare, look everywhere.
This probably isn't the answer you're looking for. Sorry. But it is the answer that sprang into my brain. And in the theme of "be you" I typed it.
It's a great question and lots of folks have good perspectives. Big hugs and your you is awesome
And still a vastly more efficient use of our resources than chemical-fest irrigated lawns.