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 ...
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:
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