In today's world, in theory you can mix and match different vendor's products because they are all NMEA 2000 compliant.
Some people do just that as it allows them to pick the best of the bunch per device. In the real world vendors put in tiny little changes to the standard that provide a better interface or 'extra' functions if the entire system is on their network.
That radar is always going to be a standalone - it won't interface properly and overlay on the chartplotter. I don't think he'll be happy with it, especially considering the 'whiz-bang' effect of the other new technology. I'd advise him to toss it (sell it) and get a RM 18 inch HD radar.
You didn't mention VHF or AIS, if he already has a DSC VHF this may be wasted typing, but - here's the one time I advise against RM and all one vendor -if he wants AIS receive capability I'd pull whatever VHF he has and install a Standard Horizon 2150x - it's got a built in AIS that will connect to the e series MFD's from Raymarine (takes some wiring).
My setup on the Gemini was a 2150 plugged to my e7d, St60's for instruments, and a ST1 to ST2 converter hub.
On the Irwin 38 CC it will be what I've advised here in this thread with a few extra's -(SH 2150x DSC VHF and AIS,
A70 (autopilot control),
X30, linear drive type 2,
18 inch HD from RM,
Airmar p79 (RM part A00170 I think) for depth and sonar,
a ITC 5 sensor pod/converter
and a Network hub (E85001) to plug my PC in.
Here's a drawing I did of my plans. I follow my own advice