I don't think riley_dog means they somehow controls Unify APs with opnsense. I think he just configured the APs with the Unify controller, the never touched them again and left all routing to an opnsense box.

This seems to be a popular approach, as there are no attractive routers from Unify, there was the Ubiquiti Unifi Security Gateway (USG), which ran very hot but was affordable and small (EdgeRouterX-like). Now they have the Dreamrouter, which has everything in one, including Wifi. It looks like an Alexa tube. There is a gap in their offering if you ask me, I'm also looking for a nice simple 2 nic opnsense box (preferably a nuc(-like)), after I blew up my EdgeRouterX (used the wrong power supply).

You use OPNsense as the router, but the rest of the equipment is managed separately.

I don't know of a system that works across multiple SDN solutions.