Kernel support should have no bearing as the apps are purely userspace apps. You can use the kernel mode if you root the phone, but that's not a typical scenario.
Well, the issue isn't kernel vs user space, but you are correct that you still need a custom ROM and/or root unfortunately. I had assumed Android had also allowed netlink sockets for WireGuard but alas they did not. So the app can't communicate with the kernel module, bummer.