I don't have any solutions at the moment, but three things come to mind:
1). Try without "--blobs",
2). Does "strace -p <pid of pg_dump process>" show anything unusual? Futex? Lots of semops?
He probably needs to find the pid of the backend to which pg_dump is connected (such as from pg_stat_activity), and strace that rather than stracing pg_dump itself.
