Depends on which muzzleloader only unit or hunt you are talking about. I believe there are a couple. Take a look at land status maps and the WG&F website under HMA and Walk in areas to see if there are other access options.
A couple of areas have muzzleloader tags. Actually 3 areas have Type 0 licenses. Some state lands may have firearm restrictions that allow the use of muzzleloaders or some HMAs and walk in areas.
I know of just a few in the state. When I was in college I hunted area 50 west of Laramie, near Woods Landing with great success. I ended up filling on a piece of state land but I had made contact with several of the ranchers around there and was comfortable that I would have a solid back up plan. I can not speak to the other areas but I know that Area 50 was not restricted to HMA or Walk in areas although I did scout a walk in area very heavily.
Obviously hunting with a muzzleloader in Wyoming can be done during the rifle season. It is a little tougher especially after some guys get to chasing them but like everything else, where's the is a will, there is a way. With that said, I would love to see some staggered hunting seasons depending on weapon type but understand that such would only cater to the very few of us.