It's "officially" incompatible, but it works fine here. Same with Reason 7. Your mileage may vary, and if you're using 9.5 then I would strongly suggest steering clear of Mojave (in fact, I'd steer clear in general for now - you're not missing much).
fwiw I've had Mojave installed for a couple of weeks and the only main differences I've noticed are...
- Dark mode. I don't use it, and now I can't set just my menu bar to be black while retaining the look of everything else. There are work-arounds but those make all your apps think you're running dark mode, which causes a load of inconsistencies.
- More audio pops. No idea what's causing it, but even something as simple as listening to music sometimes causes the audio to pop and skip for no reason.
- Some of my Wine-wrapped apps are behaving oddly. That's not massively surprising, but it is annoying.
- It broke Sylenth.
I'm sure this stuff will get fixed but I do sort of wish I'd stuck with El Capitan. In my case the upgrade was relatively painless, and all of my major stuff works (Sylenth now works after installing an update) - but I don't feel like I really got anything particularly useful out of it.
edit: related -
mooseharris wrote: ↑05 Nov 2018
VST 3.0 support might do it, AU support might do it, but I have a lot of Roland hardware and software, and none of the software works in Reason, whilst hardware facilities are limited.
I know it's not a perfect solution, but if you want to use AUs in Reason you can if you use a plug-in wrapper. Right now I'm using NyrvSystems' AgentCM which came free with Computer Music (which I bought for this very reason), and while it's a bit fiddly I'm currently using it to host DrumSpillage with zero issues. It also seems to get around the main issue I have with a lot of Kontakt instruments taking forever to load. Like I said - not perfect, but it's a workaround.