Yes, it does work.
I took out the screen of the imac a1418 emc 2544, I conncet the mini dp cable to imac thunderbolt port (the 1st port, ther are two thunderbolt ports), turn on the imac, yes, without build in monitor of the imac, the imac works straight away with the external dp monitor, of course your need dp cable, my dp cable came with Dell monitor, one side is DP, one side is mini DP, very useful.
