TL;DR: Don’t do it.
ZWave makes Home Assistant VERY slow to shut down. Unbearable. I’ve seen some talk going around about how it might be a good idea to run ZWave stuff in one Home Assistant… and everything else in another… and then link the two using eventstream.
Here’s the problem… you need state_change events to flow from the ZWave HASS to the Master HASS, or you won’t see your devices in the Master HASS. And you need service_call events to flow from the Master HASS to the ZWave HASS or you won’t be able to run automations that control any of the zwave devices.
I turned off discovery on the ZWave HASS… because I only need ZWave. But, there must be service_call events that make it go anyway, because the ZWave HASS error logs were filled with messages about how it’s trying to connect to various services but doesn’t have the credentials to do so.
The Master HASS was mostly okay. Except, none of the zwave devices worked because the ZWave HASS eventually gave up on everything. It was even complaining that it couldn’t find the input_boolean.turn_on service.
If I run either of them alone, it runs fine (except for the automations that don’t work because none of the zwave devices are present). But… both at the same time… no. Just don’t do it.