Although not quite a rhythm game, Geometry Dash can still be placed within the broader class of “timing-based games”. In particular, lowering the number of attempts in clearing a generic Geometry Dash level requires you to recognize common patterns within levels, which is very similar to how you would improve your reading ability in Etterna.
That is why I would expect there to be a decent, if not significant, overlap between the two communities.
I know of SrGuillester and Sunix, but I’m not sure of anyone else. (I personally am not involved in the GD community, although someone I knew from high school is quite well-known.)