I'm just trying to work out exactly how the endurance events are structured at FSAE-A. I know there's 2 heats for endurance, unlike at the US event, and each stint in the enduro must have a different driver, but does the second heat need to have another 2 different drivers? If allowed, would the same driver doing two heats count as one or two events?

According to standard FSAE rules the enduro counts as 2 events. Since the maximum number of events a driver can participate in is 3, that means only one enduro per driver. This is the way it was enforced in 2003.