Power M1XEP from Control Unit?

Okay to power M1XEP from M1 "+VAUX" and "NEG" pins? (Same terminal block as AC in pins)

Yes, you can power the XEP from the AUX power pins, but you need to be careful that you don't exceed the 1 Amp capacity of the M1's power supply.  The max power of all the devices you power from the M1 need to be added up to check this.  That includes keypads, input and output expanders, PIRs, smokes, etc.
 
Elk provides a current draw spreadsheet to assist in this calculation.
 
There was previous discussion of this question here.

This won't do you any good in a power fail situation if your network goes down before the Elk runs out of juice.  You'd be better served by powering the XEP off your network UPS and free up the Elk power for more useful purposes.  JMO.