Since they pulled survivors form the Montana it wasn't a given they'd be corpses.
As to passing over other nationalities to get to our American Citizens.....Why not?!
First of all, not all the rescuers are Americans and you would have trouble convincing rescuers from dozens of other countries that they should only look for Americans.
Second, it is standard operating procedure for rescuers and doctors to save people no matter what their race, ethnicity or nationality.
If we can find the bodies of these Americans that will be good, but the priority needs to be to "sanitize" these areas so that rotting corpses do not spread more disease.