It is not suggested, to ever keep Minis, with large breed horses. Too many accidents can happen.
I have known of a lot of people who do this, WITH NO ISSUE!
Also, its pretty popular to put smaller animals with horses as pasture mates.
Not too long ago we had over 50 goats, a sheep, 3 pot belly pigs, 3 donkeys, 4 llamas, and 1 horse out in a pasture together and they all got along fine. Of course these animals belonged to my uncle who was battling cancer, during his last years my father allowed him to acquire these animals and keep them on a piece of land that my father owned (32 acres). When my uncles heath caused him to no longer care for the animals my father re homed them all. I then cleaned the property and moved my horses there.
I will say I was very sad to see one of the donkeys go, I had grown very attached to him. My uncle bought him and his mother when he was at a young age, I named him Stud Muffin :). He was super sweet, very in your pocket, he was even ridden a few times.
Although this ^^^ is not what I would call normal it goes to show that different kinds of animals can be homed together with out any problems. I do agree accidents can happen but more then usual it happens with horses/animals that visibly do not get along, that is why I plan on slowly introducing him to my mare. I would not put either one in a situation that I felt was unsafe. Thank you for you concerns but I do not think they are needed here.