First a rhetorical question and then an observation.

[Gordon Gray]

I have always felt that Greer's behavior is a key to understanding the scope and "clever planning" of the conspiracy. If he is simply screwing up due too his hangover, and seeing Hill running to the Limo, waiting for him, then the ambush was not so cleverly planned, and barely succeeded. If on the other hand he was responding to a signal from the DSM, then the ambush was elaborate and he was part of a secondary failsafe option, that would insure success.