Hi Dave, and (a belated) welcome!
I'm surprised no-one has any first-hand experience.
We were considering going to Cala D'or last year, but changed our minds for the Red Sea. But I did a lot of research, and it was reasonably easy to find info about dive centers there -- though I admit knowing German helped quite a bit!
Try
here, even if you don't know German -- click on the various operations, see if they have info in English, and/or just e-mail them in English. I did that, and got several nice replies back. I think you can tell a lot about an operation by whether and how they answer your e-mail.
Or maybe
here, in English.
Or try an Internet search using "Cala D'Or" and "scuba"... you get a lot of hotel listings, but from there you may be able to determine what dive operations are nearby.
Good luck!
--Marek