The owner of the phone is San Bernadino County, which gave the FBI permission to search the phone. Pretty sure probable cause is a moot point when the owner of the phone grants you permission to search it.
Absolutely. I just think it significantly weakens their argument to admit they don't even know if they phone data will be useful. I would have thought when they are going to court to compel a company to do something they would be asserting something more than "who knows, it might be useful?" in support of their case.