The grey area here isn't whether or not a search warrant was necessary (as you say, owner permission is sufficient) but whether police officers were (should have been?) required to identify the Apple employees who participated in the search.
From what I have observed in police procedures, I don't think they are required to identify their party members or their affiliation. Ever. If there's one member of the party, who is an official, and identify as such, this is sufficient.
Unless you ask. Which I would do. "Who are all this people?" "OK, you can come in. YOU stay out."
Now, I don't think members of the party who are not officials can perform all the actions of police officers. That's, as far as I can tell, the only grey area in this instance. Can non-police officers perform a search without an officer present (as far as the reports go, the Apple guys went into the house, but the police stayed outside), and bag admissible evidence?
They didn't find evidence, so this point is moot now.
The other problematic point, as I believe I already said, is the missing or incomplete paperwork. As far as I know, police officers need to report pretty much everything they do. But Apple declined to file. So I believe the officer's action reports could have stayed anonymously on request.