If you were to believe the horror stories, you would think getting OpenITG to work under Linux would be quite a pain. License-wise it would be a better option though.
In the end, building from source was the way to go.
After a test with all the interfaces the button prototype was disassembled.
The first pad-button was tested with OpenITG (mapped to the start button) and after some tinkering it worked like a charm. Now for three more and we have a working dancepad!