i don't know if an olympian has ever competed in collegiates in the last couple decades.
Mirai did in 2015, beating out Angela Wang for the ladies title. The same year Richard Dornbush defeated Max Aaron and Alex Johnson in the men's division.
http://www.usfigureskating.org/leaderboard/results/2015/2015_us_co_champs/results.html
Currently there is a $5000 prize for the winners as well as prizes for the 2nd and 3rd place ladies.