Bill.....
The last couple of years I have used Mary's Cherry Rub....it has a pretty intense cherry flavor and along with a cherry juice mop turns out very good.
Before that I used an apple rub that I got from the Apple City Smokers........
Apple City Ribs Rub
1/4 cup Brown sugar
4 teaspoons Onion powder
1 teaspoon Cinnamon
1 teaspoon Dry mustard
1 teaspoon Salt
1/2 teaspoon Thyme, dried
This will cover 1 rack of ribs
Yes, I would say the yogurt is much like the mustard....however I add the rub first and then slather on the yogurt......I want that rub onto the meat with no barrier between. I leave it on all night and just before cooking I sprinkle more rub onto the slabs. You will find most of the yogurt sort of disappears throughout the night. Very little left on in the morning.
I personally found that if you do not add any sauce or glaze, the ribs will have the flavor of whatever you used....in my case apple or cherry. BUTTTT, I believe others have tried and mentioned they didn't seem to notice any distinct cherry flavor when using this technique.
Anyway, just another little experiment. I actually only use this technique when competing or serving no more than 4-5 slabs of ribs. When I cater and have to cook 10-20 slabs, I avoid all the extra work!