Using robot framework isn't particularly going to help you test a project written in python just because its written in python. It will help you organise your tests and make them more maintainable but it will also at some point make things more difficult for you.
I'm guessing but i'd imagine you might want to test code by calling it directly in python so using unittest2 classes or similar would be fine.
This would be less easy in robot and you might need to build a launcher to do this.
If you want to run commands and check the output then robot is great at that but you are likely to need some help from the developers to make stubs.
In the absence of much more info about the scale of the project or what you are testing i would suggest unittest2 test classes as they are the most flexible and extensible approach , as long as you avoid putting asserts in any libraries you build.
With a vehicle i would imagine you have a lot of subsystems connected via a bus (do they still use CAN bus ?) which would be something that might be a little to complex for robot , but you could still execute the same test content as long as you have the appropriate test runners and good testcase classes.