Not sure for server 2019, however I have a 2x clustered vSZ running both on server 2016 Std.
Just make sure you download the Hyper-V/Azure image with the version you require from: https://support.ruckuswireless.com/software?filter=83#firmwares
I don't believe it should pose an issue with server 2019 considering the VHD is a custom build image but as everyone will tell you to 'test test test' -
It would be great to know if anyone else has got it working on server 2019.
I do know however that when running on virtual instances, Ruckus support prefer to run on VMware. It doesn't say though that they will not support users that require it to run on Hyper-V.