The motion sensor will not function for both Arm Night and Arm Stay. However, by contacting technical support, you CAN have this changed. Though, it will require that a technician visits the home to change the mode on the motion sensor (from software on the touchscreen). When this is done, it WILL allow the usage of the motion sensor during Arm Night specifically.
I recommend against this, as any movement in the home during the night will instantly trip the motion sensor, thus sounding the alarm and notifying the Central Monitoring Station.
If you do in fact want this change done, give technical support a call at 800-266-2278 and request a technician to visit the home to set the motion sensor to work during Arm Night mode.