I never noticed when my tb was on oats. Oats will only make a horse hot if give slot but normally have to b mixed with corn or something else that's a hot feed, but all horses are different... I only know of is oats is a source of fiber but that's all
Horses tend to put on a lot of weight when on oats or a mix and they aren’t being exercised enough, they often become ‘hot’ or ‘highly strung’ as a result of oats. If you want to give your horse more energy as their workload is increasing I would look into a competition mix or get haylege as both provide more energy for the horse.