Chael Sonnen -- Ronda Rousey Could BEAT UP Rampage Jackson

Ronda Rousey won't be fighting men in the UFC ... but it's not because she can't hang -- in fact, RR could kick the living crap out of some of the UFC's top guys ... this according to Chael Sonnen.

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."