Both mine prefer hay rack (we made one from wood ourself). QH spreads the hay around looking for better leaves (I guess? :) ), so they end up eating part of it from ground, but only after they are done with hay in rack.
My horse is very prone to sand colic. I always fed him off the ground and NEVER had issues. It wasnt until I moved him from a grassy field into a paddock that had only dirt. His teeth are all loose and he's a really sloppy eater, after he eats his grain out of his bucket, he picks it off the ground and gets a lot of dirt in with it. I feed him in a corner bucket on the wall but geuss what! His teeth are yucky so he eats like an old man and drops grain EVERYWHERE. So he picks it off the ground...
The thing with sandcolic is that it depends on what your ground is like and how much dirt they are eating. Mine wouldnt have an issue with the hay, I can't see them picking up a lot of dirt with the hay, it's the grain that really causes issues. (i think). The hay will help push anythign he takes in out, that's why forage is so important in their diets. If you are concerned you can take some of his poop and put it in a bucket, add water, let it sit for an hour or so and the drain the bucket, if there is dirt in the bottom of the bucket, then you've go a potential issue and you might want to consider being proactive and adding something like sandclear to his diet.
Eating hay from the ground is more natural to the horse and opens the airways, providing your stable is clean and free from debries, its the best way to feed hay. A hay rack or net is suspended and can cause the horse to have to stretch and this can build up muscles under the neck which are not good.
My horse is kept in a yard... the soil is very loose because they walk on it all the time but I wouldn't say its sandy. Our soil is very clay-ey. She has gotten colick a few times but we're unsure why - thinking its sand colic.
I've tried feeding her psyllium but she hates it. She tries to eat it but it sticks to her toungue and roof of her mouth and she won't eat it now. Would psylium pellets be better? And could I just give them to her once a week or so?