I can only vaguely recall the show, it's long run ended when I was only a few years old and it didn't have a vibrant run in syndication.
The animated opening did stick with me, though.
Cursory googling is no help on production credits. I'll hazard a guess that it was John Wilson who did the Sonny and Cher animation (and the open titles to "Grease").
I'm a great fan of this era of animation. I love the loose but detailed designed and the idiosyncratic animation. Budgets were obviously tight but the tricks developed by UPA and John Hubley, amongst others, to stretch resources while maintaining strong character work.