Yes, for sure.
We haven't played a ton with animal companions in 4E and while they seemed effective enough, they didn't seem the best build. Anyone going for that build seemed motivated more by a desire to add a little color to their PC then to min/max it.
So, I'd certainly let a player get a little more out of their animal companion.
Even if with further play the 4E companions were on the potent side, I don't think I'd worry much about letting them use it as a mount. It still is more of a utility thing.