You can’t load modules built with a different compiler.

Sure you can. There's even multiple guides for how to write C++ kernel modules, which inherently is going to use a different compiler than what was used for the kernel itself. BOSS Linux even writes C++ kernel modules.

if you want to use a module wrote in rust you also need to have built in the rust support in the kernel

Only if the module uses rust-specific interfaces in the kernel, otherwise it can be assembled into a .ko to have plain C-style symbols loaded by the kernel like normal.