Yeah, there are photos of him with the Embassy. Don't know if it's on any recordings. The story I heard was that in 1967 Terry Melcher wanted to use studio musicians on recordings and that made Fang and Drake unhappy so they left. No idea if it's true.
It wasn't just the absence of the prominent bass lines after Fang. They also softened the music, made it more pop than rock. I didn't like any of the post-Fang era songs except Let Me. I didn't like Mark Lindsey's solo stuff, Arizona and Silver Bird, catchy pop tunes but just so cliched. Same with Indian Reservation. It didn't sound anything like the early songs, and supposedly it was actually a Mark Lindsey solo track that got released as a Raiders tune.