No, the only difference from shooting at most hunting distances (at least for me) with iron sights and using a scope is you won't get your pretty little 1" 5 shot group. Like was said above, keep it in a kill zone sized area, and you're fine. I like to use a paper plate, the 7-9" plates do just fine for telling you if you can hit something.
There are very few deer or hog with 2" kill zones, so don't worry about making the perfect groups and just make sure you can get it in the zone. My .30-30 doesn't have a scope on it and it does just fine at the distances I usually hunt, which is 50-100 yards.
If you're planning on 300 or 400 yard shots, you might want to practice quite a bit, but up to around 150 yards, you should be ok.
Edit: Forgot to add, this past weekend I shot my new muzzle loader for the first time. At 50 yards (with open sights) it was shooting 3" low right out of the box. Moved the rear sight to aim up, dead on. Next week I'll test it at 100 to find out where I need to aim when I'm shooting 100 yard distances, but I'll leave the sights set at 50, because both of my stands only have shooting distances of about 50 yards around them.
