No they cannot. There engines are mounted too low to the ground (since RJ
's are low themselves) that they were not certified for pushback for the same reason why 737s, A320s, etc. are not certified for pushbacks. The issue is that they kick up a lot of debris which can injure ground crew and cause other damage, even to the plane itself.
Not really an issue for aircraft like the DC-9, MD
-80, Fokker F100 because the engines are mounted quite high.
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran