A dirty bomb in a container or tanker? Meh, no biggie, not worth upsetting the "little people" by mentioning the possibility or the fact that we consider it a real enough threat to be actively looking for anything like that.
No, I completely agree, the Saudis could absolutely know, then tell us NOTHING.
But again, if we had our fears and wanted to check, why not simply do so at sea, with a chopper..?
Or have some SEALs do board fantail of the dubious vessels from a souped-up Avon raft..?
In other words, why perform the load check using a ship COLLISION..?