Thank you FD, at last a useful post. In fact the procedure of monitoring and advising errors is common here as well - most self-interpreted approaches (including visuals) are routinely radar monitored, certainly in the UK, and similarly warnings would normally be issued if a major error was seen (as has happened at LGW a few times!) The problem here is that we really have no idea when precisely the 'dirty dive' happened or when the controller might have been realistically expected to recognise what was happening as an imminent accident - or merely as this apparent 'scud running' as described earlier which appears to be 'accepted'.
Perhaps he was used to the heroes coming in under the crud at tree-top height? When to shout?