Will returning a creature trigger Prowess?
The creature with Prowess has to be on the battlefield to trigger it.

Prowess is a triggered ability that only works while the card it's printed on is on the battlefield, i.e. as long as it's a permanent. Therefore, if you return Lotus-Eye Mystics with Rally the Ancestors, the Mystics will not get the Prowess trigger from that. 

You will, however, get the enters-the-battlefield trigger from the Mystics.