Can an induction motor be used to generate power?
Induction motors make very good generators. They are the typical generator used in wind turbines for instance.

Let's look at the speed torque curve. Here's one from electrical4u.com



Speeds in the 0 to ns, standstill to synchronous, are normally the only speeds people consider.

Normally, an induction motor operates at full load with a few percent slip. Consider what happens as the torque delivered by the motor drops, the slip reduces, and less energy is drawn from the supply. As the torque drops to zero, the speed rises to synchronous speed, and no power is drawn from the supply. 

If we now increase the speed above synchronous, driving the motor externally, torque is required to turn the motor, and energy is delivered to the supply.