The Ecobee thermostat integration is a back end integration, and you should be able to use it with both Alarm.com and whatever other compatible automation system desired.
There are limitations to Ecobee in Alarm.com compared to Z-wave thermostats.
Alarm.com and Ecobee integration does not support the following features:
- Thermostat scheduling
- Thermostat rule-based automation
- Remote temperature control or averaging using Alarm.com temperature sensors
- Aux Heating Mode (for heat pump systems)
- Non-thermostat ecobee devices (temp sensors, motion sensors)