Rifled slugs are spun/stabilized in the air by the rifling cast into the slug itself, from what I understand. So, no you don't need a rifled barrel unless you're looking for long range (100+). Modified choke and you should be good. I went put several through my 870 at the last Hicksville meet. They leave nice big holes behind.
Here's the feral hog that was rooting my yard. 00 buck at 40 yards.
As I said earlier, I'm considering it as a solution for "oh shit" encounters. Not as a hunting weapon. As for the choke, I have no idea. It's the factory choke that came in the barrel, and I've long-since lost the choke removal tool. It's sounding like .00 buck is a viable solution, though. I've used it on coyotes but have yet to line up a shot on one of the hogs that are beginning to move in. I simply wasn't sure if buckshot would be effective on a hog before I started this topic and wanted to explore options and learn a bit.