I have no experience with the HDL Nordic rpi server, so you should check with HDL if you can use RPi hats on their product.

I have iRidium and Zway server running on a single RPi with the RazBerry HAT. They communicate over HTTP API, so you could also run them on separate RPi's.

https://z-wave.me/products/razberry/

We prefer to stay away from modem type boxes and stick with DIN-rail modules to keep the install neat. There are multiple options for RPi, but I've never seen DIN-rail enclosures for other Zwave controllers.

Also an option is to a RPi with RazBerry addon. iRidium can also run on the same RPi or separate. I choose this option so I could stick with DIN-rail modules and put a RPi in a DIN case.

Thanks. No rush, but I think this might get more in demand in the coming period. Especially if the wall-panels become more affordable this way. So we'll see if the voting will help.