Is feedforward used in boost converter operating in DCM mode?
The only "control" in this circuit is that the DutyCyle of the switch is somewhat related to the input voltage. This would only work properly if you would have a fixed load. If you remove the load, the output voltage can increase until something breaks. That is not "proper control" in my opinion.

This is a CCM or continous mode or PWM  (Pulse width modulation) converter meaning it keeps switching all the time.

You could operate it in DCM or discontinous mode or PFM (Pulse frequency modulation) but during the off period (when it is not switching) the output voltage will drop. When it drops below a certain level the switching has to start again. But how do you know when to start switching again ? There's no feedback. So although I think it is possible to operate this converter in DCM/PFM I do not think it is very practical.

In a proper converter so including voltage feedback. It would be sensed when the output voltage is getting too low in DCM/PFM. The reason why some converters can switch between CCM and DCM is to save power when the load sometimes requires a high current (we use CCM) but sometimes requires a low current, then we use DCM to save power.

In my opinion this feedforward is more a theoretical example and not something you would encounter in a real design. In that respect CCM or DCM does not really matter that much.