Crossing the border on arrival at Schiphol Arrivals 3 on Sunday, there were only 2 Marechausse booths open - and the guy in the EU/EEA line was busy talking sporadically with a colleague hanging around behind his booth for most of the time.
A bank of e-Passport readers to the left that had all been lit up in red (and thus closed) suddenly opened by the time I reached the top of the queue. So it seems that they CAN open the e-gates when they feel like it.