Rick,
My quick answer...NO. A centerfire and a muzzleloader are both "rifles".
Scopes with their reticle specially designed for muzzleloader trajectory ( like the Bushnell DOA 250 ) definitely have a big advantage for shooting beyond 100 yards with a muzzleloader. I have that particular Bushell mounted on my "long range" smoker, but my .45 CVA Apex (which is my primary hunting smoker) has a typical "rifle" scope on it with duplex crosshairs.
Scopes that are labeled "muzzleloader" are usually lower power variables for obvious reason, but may also be beefed-up to handle higher recoil.
Many accuracy problems are not due to the rifle or load, but improper scope mounting or using cheap mounts. As far as quality goes, you get what you pay for. A cheap or economy scope can cost you a trophy, and it's a very hard lesson to live with considering you may only get one chance in your lifetime. My advice is to spend as much as you can on a scope. The scope market is very competitive, and the price generally reflects the features.