I think the issue is that an after-market 360 view system (consisting of four cameras, wires, and software to merge the images from four cameras into a single bird's eye view) is an integrated system and thus likely would not be able to use existing standard rear-camera. So you probably do nee to replace the OEM camera with the one that comes with the after-market system.
I responded to a recent post in the Infotainment topic. I really value the 360 degree view - it was not offered in Canada for 2019, so I waited for 2020 to see if the 360 view would be offered on the 2020 Signature trim in Canada, and it was.
But if it was not available from factory, I would likely simply live with the rear-camera only.