By chance, I tried installing CUDACPP through install cudacpp inside MadGraph v3.6.4 (which as of today is not officially supported, see the version info file.
I also tested one process and it works...
Is it supposed to install it anyway? No warning/error was displayed during the operation.
I would at the very least print a warning, given there may be incompatibilities.
On the contrary, on v3.5.11 the installation doesn't even start, and it fails as expected.