We broke the story ... Ronda just became the very first female to ever join the UFC -- after skyrocketing to the top of the female MMA ranks in Strikeforce.
Now, Chael -- a seasoned UFC vet -- tells us, "I'd like to congratulate Ronda Rousey on becoming a pioneer in this sport. It's well deserved and overdue."
He adds, "Looks like Mitt Romney has a new favorite fighter and Rampage Jackson has another opponent he can't beat."
Smells like a challenge ...