Salmonking...no you cannot use a shotgun in place of a blackpowder rifel in a blackpowder only hunt. (XXXM series hunts). I have been slowly working my way towards bowhunting and have really enjoyed BP hunting.
Given the OR muzzleloader regs, you are basically not going to find a gun that will shoot much beyond 150 yards with a marksman behind it. For the average Joe, 100 yards will be pushing the limits of both shooter and weapon.
I have taken two deer with my muzzleloader. One was at 25 yards and the other at 15 yards. I pretty much hunt as if I had a REALLY high powered bow.

Full camo, face mask, gloves, etc. I have friends that 'road hunt' during BP season and are suprisingly successful.
Overall, it is probably not as demanding as archery, but it0 is not a cakewalk.