It is not correct.. Bob Yannes wasn't involved in the Amiga's design in any way. It was a team totally outside CBM (and Yannes had left CBM anyway soon after the C-64 was completed in 82).
The Paula isn't really a synth chip at least not anything like the old Ensoniq synths or the SID chip. It only plays back samples.
I'm afraid I can't help with the designer's name. Probably that's written in some Amiga history article on the net.. It could have been Jay Miner, but I only know for sure that Jay did the Agnus.