The criteria for Pistoleer hasn't changed since it's introduction (to the best of my memory):
Men’s and Women’s Pistoleer: Shooters are restricted to the use of percussion revolvers, pre-1873 percussion or original/authentic reproductions of rimfire cartridge pocket pistols, exposed-hammer double-barrel shotguns (percussion or cartridge), and reproduction or original pre-1873 pistol-caliber repeating rifles (e.g. 1860 Henry, Spencer, 1866 Winchester, etc: Shooters must shoot blackpowder or approved blackpowder substitute powder in all firearms except those chambered for rimfire cartridges. Pistols and revolvers must be shot one-handed. Pistoleer shooters will shoot the same course of fire as the other competitors except that in a stage requiring more than two shotgun rounds the Pistoleer shooter would not be required to shoot the extra rounds.
Essentially, this means Pistoleer will only fire two shotgun rounds per stage...no-one has ever been disadvantaged by loading the ML shotgun in this class.
My experience has been limited only to NCOWS competition at the National Shoots...over the past years I've maybe seen four muzzleloading shotguns used in this class. So, I'd say the majority in this category have used breach loading hammer guns.
Slim