Yeah, Animal' capable of it - you said it yourself - the EM have done mellow songs.
Animal is first and foremost a drummer. A wild one, but a drummer nonetheless. He's never been described as a monster or creature or whatever...always a drummer. Despite his eccentricities he can keep a beat; i think just the joy of hitting something outweights his desire for tempo - the fast wild numbers are just a particular thrill!
Of course that doesn't mean that he's ALWAYS going to behave during the slower songs...Sonny, the classical opening in Zero Mostel episodes, numerous songs that end with a extra Animal flourish, Dudley Moore closing number...i also suspect that over the years Floyd has come up with techniques for mellowing Animal beforehand!
And it's not like Animal doesn't have his mellow sensitive side - he cries, he meditates, he loves to cuddle with bunny rabbits, he cries singing Danny Boy; he's not just a crazed ball of energy that can't handle the slow stuff.