With 2 Z-Nets you would need 2 instances of Z-wave-JS UI (ideally). You could use 1 Z-wave-JS UI and 1 Z-wave JS, but I wouldn’t recommend it.
This post Zwave-JS-UI on Znet via docker - Configuration / Z-Wave - Home Assistant Community (home-assistant.io) shows how to run Z-wave-JS UI directly on the Z-Net. If I were to add a second Z-Net I would go this route. Then you can add a second Z-wave integration and point it directly at the Z-net. If you did this on both Z-Nets you can eliminate the Z-Wave-JS UI Addon.
Not for the faint of heart, but if you’re reasonably technical these are step by step directions. @goldriver has posted here and the HomeSeer forum on how to get this running.
If you copy your Z-Net image before starting it should be to recover back to square 1.
Maybe someone can make an image and host it of these mods.