Both players had to make a decision to stay in school or remain in the draft by Wednesday.
The 6-foot-11 Diabate started 26 of 32 games for the Wolverines, averaging nine points and six rebounds. He was born in Paris and played high school basketball in Florida.
Houstan, a shooting guard from Mississauga, Ontario, led Michigan with 60 3-pointers, averaged 10 points and started in every game last season.
The Associated Press contributed to this report.