No you can’t control the volume of the Naim streamers as Naim do not expose it. They also recommend not to use the volume control on them as it’s purely to get Airplay certification and effects the SQ, they say you should use a PreAmp to control the volume not the.device itself. As for power that depends again on what Naim allow Roon to interact with. I imagine it can control the power on as it does with my Atom but there is no control to turn it off.
Other solutions to control the volume would be to add a Harmony Hub remote control. As you can then add a Roon extension called Deep Harmony that can allow the Roon app to control playback on the streamer and manage volume on another device such as a preamp or other amplifier. This is how I control one of my endpoints and the active speakers attached to it.