I tried it and had some success.
1. Put event that has tablet with green screen display on top video track.
2. Put event with background image that will fill the tablet screen on track below.
3. Apply Chroma Keyer FX to event on top track.
4. With timeline cursor at beginning of event, apply Motion Track (Bezier masking FX) to event on Top track.
5. Apply Picture in Picture FX to background event on lower track. Adjust to fill tablet display on top track.
6. Select both video events (top and bottom) and apply script . Tools/Scripting/Copy Motion Track to PIP
This does work but left me thinking it would be better to play the video on the tablet and shoot that live. If that’s not possible, this method might be second best.