The Diamonds Are Forever movie appearance I'm familiar with, although I didn't know who Dean was years ago when I first saw it. I actually think that's one of the worst Bond movies. Sean Connery, after giving up the role to Lazenby for one movie, came back and did this one. Unfortunately. Connery never looked worse in a movie, and seemed very over-the-hill in that film, for such a relatively young actor. Afterward Connery gained an aging elegance in a series of movie roles over many decades, that cemented his place as one of the great lead actors.
Diamonds Are Forever was also very trite and silly throughout, with a lot of sweaty out-of-shape actors in tacky polyester clothing, and exceptionally cheap low-budget looking sets. Even Jill St. John was disappointing and a chore to watch. That and the Lazenby film that preceded it were among the weakest links in the franchise. The other weakest links for me were A View To A Kill and the two Timothy Dalton films.
The movie after Diamonds Are Forever was Live and Let Die, the first with Roger Moore, and a fantastic return to greatness for the bond series, with the best Bond movie theme song by Paul McCartney of the series. A great introduction to the Bond franchise, and the first I saw, on its release in 1973.

Over the years, I've recorded all the Bond films on DVD, so until the next film comes out I have a complete run of the film series.

But yeah, Jimmy Dean has a role in the movie, and he was one of the better parts of the movie. Beyond his musical talent, Dean was also a gifted comedian.

His "Big Bad John" single I never heard before!