NX8 is (in most cases) compatible with Alarm.com. You would need to get a NX-400-US-VZ or NX-400-US-AT Alarm.com module. These cellular modules state:
Compatible with NetworX 4,6, 8 and 8E. (Note: certain older V1 NX4, 6 and 8 may not be fully supported).
Are your sensors wired or wireless? If they are wireless and you don’t want to use the NX panel then you may be able to use those sensors with a Qolsys panel instead if you want. Qolsys has a much brighter future with Alarm.com than NX in my opinion.