They did not want to pronouce him until his Mother got there. Why would they pronouce him as soon has he got there? Someone had to tell his kids and they wanted Mrs Jackson to do it. And let's be frank they only worked on him because it was Michael Jackson
Many people are pronounced dead as soon as they arrive to the hospital. Just because he is pronounced dead among staff does not mean they have to immediately tell that to the family. They can still hold on to that information until Kath got there, then tell her once she arrived so she can tell the children.
Even if they worked on him simply for who he was, the records will show what they did and MAY give insight into their thinking on the person when they arrived. I donot know what they thought myself. But I don't see them futilly working on someone, even MJ, if he was clearly dead. Why work on a corspe?