Is the only 10W-30 oil approved for use in Ford 6.0 diesels the Ford brand oil?

No.

It's best to use full-synthetic diesel HDEO in diesels, particularly in turbos. Amsoil makes one of the finest 10W-30 diesel oils, which I strongly recommend:

AMSOIL - Synthetic 10W-30/SAE 30 Heavy Duty Diesel Oil (ACD)

Several other recommended diesel engine oils are mentioned in the link below:

https://www.askmehelpdesk.com/cars-t...ml#post1415281