Ronnie Williams introduced Frank Zappa to Paul Buff in 1960. His contributions can be found on a couple of early Zappa recordings.
According to the liner notes in The Lost Episodes, there was no contact with Frank until 1975 when Ronnie showed up to a concert in Pomona. After requesting the "song about the boogers" he was invited on stage.
Bo Salisbury was an eyewitness:
"I remember it as plain as day. Frank looked down after the request was shouted out, laughed and said something like, "It's Ronnie Williams!" As I recall, he was in the center, about 6-8 rows back, and Frank invited him up on stage... Denny Walley was playing bottleneck most of the night on a Telecaster, took it off and handed it over to Ronnie. They played the song, the audience cheered, Ronnie gave the Telecaster back to Denny and the show moved forward. It was great."
-- info from Bo Salisbury