I disagree. When Belloq saw the activity from afar in the early morning light, he saw movement, a large enough box and the tripod thingy used to lift with. Indy was putting on his hat at dusk and they were still digging into evening.
If they were seen at that stage, the hat would not have been the giveaway. It is the fact that a whole crew was still working in an unusual area when everyone else on the site had finished work for the day. But they obviously had to take the risk.
Because it is just dawn when Belloq and the German officers see them, we assume it took all night to get the Ark out of the Well of the Souls. It is the fact that it took so long to get the Ark out that they were caught. They were caught because they had to work out in the open. Indy, hat on or not, was racing against time and having to do something in plain sight of the Germans and he didn't quite get away with it, in typical Indy fashion.
So, nothing ludicrous here. How dare you! Slap!