if it is natural youghurt, although flavoured it is fine but i would not give normal flavored youghurt (preservatives etc), only natural, natural youghurt has some great natural cultures in them that are good for the gut flora in all of us.. i dont buy plain youghurt only flavors such as mango or peach etc and they are all natural youghurts, natural being brands with no additives, preservatives etc. and they have cultures in them such as acidophilus and lactobacilllus.
charlie loves them and gets to lick out the containers when i finish, i dont give her a bowl full of course, she just gets to lick out my empty containers and licks the lids, but it is at least a tablespoon worth and it doesnt adversly affect her.. dogs dont generally dont deal with lots of dairy well, lactose intolerance etc. so only small amounts should be given.
but i never started giving it to her for health reasons, i did it as i found i didnt want to waste any food so if she licks the containers i dont feel anything is wasted and we all can enjoy it. oh and she look so cute with her head buried in a 1litre youghurt container, and when she comes out she has it all over her nose, just too darn cute.