Roles shouldnt be put up as rust, but there is clearly rust in the github repository. Its not a lot but my understanding is the usage is somewhat growing.
According to the gitlogs this conversation happened about a year before those were added. We talked about this pretty point blank. It was made clear that while they might use rust in the future and they had rust fans internally, it was a go position.
https://github.com/gravitational/teleport/search?l=rust