[R0b0t1]

Yes, there's nothing more challenging about using Linux for hard realtime. You still need to address your IO to ensure realtime constraints but you have the benefit of already constructed realtime ethernet drivers, etc.

It's also common to run your code as init and avoid calling into the kernel.

A more modern treatment is to write whatever and then qualify the system thoroughly, and all things considered this will probably overtake everything else as the main development methodology.