Dave Wyndorf, songwriter, lead vocalist, and a guitarist for Monster Magnet, explains in an interview with Adam De Ville for Collide:
Adam De Ville: “Dinosaurs in Vietnam!”
Dave Wyndorf: Yeah! I just pictured a T-Rex stomping through Vietnam and chomping
everything up during the war. I made it all up on the spot and Dave
Sardy was totally into ...
Personally, legal issues apart, I don't think Ozzy is actually capable of performing Dio songs.
Dio has a much more powerful (possibly operatic) voice and I think he also has a greater vocal range.
Many singers are now not even capable of singing their own songs from the past. A good example of this is Ian Gillan of Deep Purple who's on record stating that ...
Dio and Ozzy didn't part on the best of terms to put it politely. Copyright issues flew around. Dio isn't allowed to play Ozzy-written songs either.
Apparently, things are beginning to heal.
Quote from the link:
"They say that we're the anti-christ. Well, what makes them any
as requested by OP, turning this comment into an answer :
On the strict meaning of the word, it suggests he is more than just laying down/keeping the beat, but rather has some role in how the piece is orchestrated.
If I knew Black Sabbath's music in more depth, rather than part of the soundtrack of my life, I could expand the answer with examples.
References in the wikipedia article about the album Black Sabbath lead to this page about the phoshoot location.
From that page:
"Not much is known about the eerie woman used in the photo other then
she was a model/actress hired for the day and her name was Louise."
From another page some more info
Johnny Morgan and Ben Wardle write: