That's routing inside that mixer, right, that's where you have a stereo pair of inputs and outputs that are RCA? Have to see if it can do that.
But yes it should work. When you hit VSTconnections in Cubase you would need to add an input bus and a return bus or set that up as an external instrument. What shows up when you make a new bus, what's the list of available I/O? Does those RCA jacks show up there?
Not sure of the capabilities of that mixer.