If the salvors were responsible they would have definitely been reluctant to use third party barges you are right. These are the barges that were offered, I would have assumed they would anchor them at a safe distance, pump oil from the holds (reach hoses over with ship cranes?) and tug 'em back to shore.
There are many possibilities as to why they were not used, here's hoping they sort something out soon though, that spill is getting nasty!
As Mike Skyrme pointed out, shipping containers semi-submerged are the icing on the cake. Madness I tell you!!