Dio, who died in May 2010, had spells singing in Black Sabbath and ’80s metallers Rainbow as well as a lengthy solo career.
His widow, Wendy Galaxiola, confirmed that the album is unlikely to be released this year but that all the artists were in place, reports Noisecreep.com.
Galaxiola said: “We have a tribute record, which probably won’t come out this year, but everybody signed up.”
Halford will add vocals to a new recording of Rainbow’s ‘Long Live Rock ‘n’ Roll’. Motorhead’s Lemmy and Skid Row singer Sebastian Bach are also confirmed to take part.
Grohl’s band Foo Fighters headlined the NME Awards Big Gig on Friday (25).