I have heard of them. Here is what I was able to find. Great information
What is a Drum Horse?
The Drum Horse is actually named after the job it performed. Their main use was and is by the ceremonial British cavalry as part of their regimental band. These horses carry two solid silver kettle drums--plus a rider--during the Royal Parades. As much as 350lbs! Drum Horses must be big and powerful to carry the great weight. Drummers control the horses with reins attached to their feet. So an excellent temperament and lots of patience on the part of the Drum Horse are a must as well!
Prior to 1998, the Drum Horse was basically unknown in America and they are still quite rare. They are usually the result of breeding two Drum Horses together or by breeding a Gypsy Horse to a Clydesdale or Shire. One of the associations allow Fresian's as well. This crossing is done to combine the size of the larger Drafts with the feathering and coloring of the Gypsy Horses. The Drum Horse makes an athletic, even tempered mount that can be competitive in many disciplines.