Rifled slugs are made specifically for use in smooth bore ... and will safely pass through any standard choke diameter up to and including Full.
As previously mentioned by others, in general the smooth bore-rifled slug combo is not as "good" a set up as a typical rifled barrel and a slug made for rifled barrels. This is because it takes a bit after the slug exits the muzzle for the "rifling" to produce the stabilizing spin and the energy lost in the friction between the air moving over the bullet's "rifling" reduces the down-range foward energy of the bullet significanly. In addition, the rather blunt shape of the bullet, plus the heaft of the bullet and the moderate muzzle velocity all combine to produce a rather dramatic arc. You can get a feel for all of this at the range.
The effective range of the rifled slug will be about 75 yards. Sure, folks have killed deer out farther with a 20 ga. smooth bore and rifled slugs .... but 75 yards is a good max limit to think about. If you could pony up for a rifled barrel, you can just about double that effective range. And inmy view, if your eyesight is good and you are competent with open sights ... say to 125-150 yards, I'd spend the $$$ on a rifled barrel and buy the scope set-up down the road. But by all means, if you decide to go the scope route, don't scrimp! Buy the best that you can afford. It'll be $$$ well spent.
Good luck and have fun.