I would say yes because well it'd be like a human riding a centaur, though it might be fun, not real sure an Andalite would let you. Like centaurs they would have too much honor and find it as an insult to do that, I mean Elfangor was taken back when Loren did it. And besides if you just hopped up on one's back, you mind find your head on the ground after a meeting with that dangerous tail.