Can you plug in a controller and still submit as a PC speedrun?

Most PC runners, by far, use both keyboard and controller. The leaderboard split is mostly due to the massive difference in loading times and the ability for PC runners to have a load remover/autosplitter. So you're free to use whatever input device you want. Some crazy people like me decide to use solely keyboard, but use whatever you feel like is the best device in any given room/chapter.