Ribs in Slow Cooker, then finished on BBQ?
While you could do this. A better method(Provided you have an enclosed grill) would be to set your grill up for indirect heat and slow cook them on your grill. This is how I do ribs and it works amazingly.

You'll have to do things slightly differently if you have a square or round grill. For a round grill try the following:


Place unlit briquettes around the outside of the grill about 3/4 of the way around. 
Start about 12 briquettes until they have ashed over, place them at one end of the circle, put a few (2-3) pieces of smoking wood chunks on top of your coals.
Get your grill temp to about 225-275 degrees F and adjust your vents to keep it there (Start adjusting before you get to your desired temp, it's easy to shoot past it).
Put your dry rubbed meat on the grill opposite your set of lit coals (do not sauce, if you want sauce put some on at the end).
Cook 4-6 hours until the meat bends easily at about the third bone when picked up from the end.
If your coals burn too far under your meat, rotate your rack to keep the meat opposite the lit coals.


If you've got a square grill than you probably cannot do the ring method I've described above, instead you will have to figure out how to do indirect heat a different way. A set of banked coals on each side with the meat in the middle or some lit coals placed in the center of some unlit ones on just one side. You need something that can keep a constant low temperature and burn for 4-6 hours. Experiment and see what works for you.