Might be possible that they were using dreamcast controllers during initial development:
Previously, Sega had developed a version of Windows CE for its Dreamcast console to be used by game developers.
https://en.wikipedia.org/wiki/Xbox_(console)#Creation_and_development
Gates was in talks with Sega's late chairman Isao Okawa about the possibility of Xbox compatibility with Dreamcast games, but negotiations fell apart over whether the Dreamcast's SegaNet online service should be implemented.
https://en.wikipedia.org/wiki/Xbox_(console)#Initial_announcement_and_content_acquisitions
https://web.archive.org/web/20170825063139/http://kotaku.com/5447897/how-xbox-could-have-helped-the-dreamcast-survive
Might be possible that they were using dreamcast controllers during initial development:
https://en.wikipedia.org/wiki/Xbox_(console)#Creation_and_development
https://en.wikipedia.org/wiki/Xbox_(console)#Initial_announcement_and_content_acquisitions
https://web.archive.org/web/20170825063139/http://kotaku.com/5447897/how-xbox-could-have-helped-the-dreamcast-survive