Its designed around the rifle primer, so not legal. Even if they had a percussion cap option, I doubt the primer is exposed to the elements. And its MSRP is $1295.
"Remington reports: “The Ultimate Muzzleloader sets a new performance threshold with the use of a closed breech system that provides a cleaner and hotter ignition. The AMP (Accelerated Muzzleloader Performance) ignition system uses a uniquely-sized brass case with a Remington 9 ½ large magnum rifle primer that is push fed into the breech plug creating a gas seal in the flash hole of the primer (see cutaway below). The result allows the shooter to load up to 200 grains of powder for increased range, energy, and on-game performance."