The 920xt cannot be used with Zwift, but can be used at the same time since ANT+ allows multiple connections.
What ANT+ app? If it is to re transmit ANT+ data it will also not work
The Garmin foot pod is ANT+ and I am guessing you also have an ANT+ only Garmin HRM which is fine since Zwift on Android supports ANT+ connections: ZwiftGame Android FAQ (v.1.0.50775)