With most ESC's used for DIY builds like this, you need to throttle calibrate them before using...it's not something that you can do from the NAZA, and should be done even if you aren't flashing or otherwise changing the programming on the ESC's. Uneven motor arming (or no arming at lower idle settings) is one of the common side-effects of ESC's that aren't calibrated. The trick of upping the idle setting in the NAZA can get around it, but it may mean you're not getting the full range of throttle to use when flying, and throttle application can be uneven from one motor to the next.
The process basically involves connecting each ESC directly to the throttle channel of your Rx (not to the NAZA) one at a time then powering the ESC on (not the whole rig) and setting your throttle endpoints. This vid gives a quick demonstration of that procedure (power on Tx, push throttle to 100%, power on ESC, push throttle to 0%):
https://www.youtube.com/watch?v=DfTdCVwZYHQ
I imagine that DJI's ESC's are pre-calibrated enough that you don't need to bother with them, and that's why you didn't run in to this on your 550.