What’s the best type of adhesive to use for gluing nitrile rubber tread to aluminum wheels?
I’m assuming rivets and zip ties don’t count as adhesives. 
You will want to rivet them so you can remove worn out tread. If you got any questions just email me.
I was going to say.
Your best “adhesive” here is almost definitely rivets, unless you want to replace your entire wheels when your tread wears out.
If you really, really want an adhesive, you might try VHB. Properly cured that stuff isn’t ever coming off.
If you’re stuck on adhesives (pun at least semi-intended), the obvious choices are CA (Cyano-acrylate), rubber cement, Gorilla Glue, Eastman 910, and Shoe Goo. I have not attempted such a bond, but I suspect that CA is too brittle for this application and would provide poor grip on the rubber side. I also suspect that Shoe Goo (which is designed to keep soles from peeling away from shoes) is most likely to satisfy, followed by Gorilla Glue and Eastman 910. Rubber cement isn’t really that strong, but it always comes to mind in situations with flexible/torsional stresses. If your aluminum has a shiny finish (as most 6061, or 6063, and 7075 items do), I would suggest adding some texture to the surface with an etching acid as though you were preparing to paint it, so the glue can get a better grip. If you have a cast wheel, you may be OK with the finish.
Repeat: I have not attempted such a bond, but in the absence of better info, and if I decided that I did not want to do rivets, this is what I would try.
Buy it in a preformed loop and stretch it to fit over your hub. No fasteners or adhesives needed.
Square-profile o-rings (stack up several in parallel)
Flat bands
(MANY more options if you use urethane instead of nitrile)
Our team had really excellent luck using hardware store double sided tape to make drilling and riveting easier and stronger. The tape holds the nitrile in place while you drill and rivet, making it less squirrely. It makes it considerably easier to get a very snug fit against the wheel and it also has the added benefit of reducing the shear load on the rivets quite considerably. We had relatively shallow flanges (performance wheels) and we had a rivet every third with extras where the loop ended. Properly installed, our tread would have held without the tape. It’s just much easier with the tape and more secure in our experience.
How much larger should your hub be than the rubber ID, in your experience?
About 30% larger according to this spreadsheet. I’m not sure if it scales up to the 4-6" range though.
I’ve installed urethane replacement tires on a 16" bandsaw. The tires are about 15% undersized. Maybe interpolate between this and the resource Mike linked?
Back when I was racing bicycles, I use 3M weather strip adhesive to glue my tires on. It is basically a strong contact cement. Changing the tread will be a bear.