The SS would never have done this, unless the candidate had already been secured in the place, and the SS already had a secure perimeter around him.
"who in the Obama camp went to the Secret Service and said, 'hey lets speed things up here, loose the metal detectors.'"
Don't matter. The SS doesn't take orders from candidates, their staff, or anyone else. The SS does as they see fit to protect the candidate.
"Lawrence, head of the Police Department's homeland security and special operations divisions, said the order -- apparently made by the U.S. Secret Service -- was meant to speed up the long lines outside and fill the arena's vacant seats before Obama came on."
The secure perimeter was already in place. The PD was simply dragging their butts scrutinizing folks for the outlying seats for inconsequential items that could only be used against another outlying seat holder.
That only applies to the President and Vice President. A senator/candidate under protection can refuse it at any time and they can also refuse to follow SS directives.