Oats are safer to feed than most commercial feed products, including safechoice. They are a pure "whole food" that is healthier for the horse. If you're feeding quality Timothy hay, oats are actually the perfect thing to "balance" the diet. The only thing you'd be low in is Vitamin E and Calcium, and not by a lot. Adding some Alfalfa pellets remedies that.
As long as the horses are in good condition, their coats have a glow, and the hooves are strong, then you can be assured that the horse's diet is fine.
I feed mine an extra vitamin supplement and some flax, but their diet needs it. Without it, their coats aren't as shiney as I'd like and my mare's hooves show some minor surface cracking. Oats and Alfalfa in the amounts I feed aren't enough to balance their diet. Now, if I decreased the hay and doubled the oats and alfalfa, they'd probably do better, but I prefer to feed enough hay to keep them busy most of the day