DevilutionX adds gamepad support so maybe that is what he is using. Of cause the PS1 port also had it, and there is also a more vanilla mod available from when the controller code was first implemented (xinput only).
I would say the Rouge is the best class for playing with a controller, it's both what I have tested the most, but also my preferred class ... which might create a feedback.
Controller support definitely has me interested. I'll check it out soon. Thanks for the info.