AFAIK binds Roon itself to all available networks (VLANs, multiple adapters, virtual adapters, …). There is no way to configure Roon to not do that (but there is potentially a blacklist for very specific network {adapters} built-in?). So if at all, you may have a routing and or firewall problem IMHO.
Notes: What is not supported?
You should be able to use the Windows machine as a remote GUI to control Roon if you allow the relevant tcp traffic to flow between the two VLANs. It is normal though that the audio device detection, based on zeroconf multicast packets, is not traversing network boundaries. So if you didn’t take that into account and implemented a solution for that problem, then I’m actually more concerned about the cases where you say it works anyway, than about the cases it doesn’t.
Maybe you just missed (to tell us) some vital parts about your network configuration?
PS: This is based on forum posts but also on my own experience with multi-homed Linux based Roon Cores and Windows Roon Remotes.