Hi,
The way i understand it is:
1. Your controller settings will send out velocity values according to how you play.
2. Applications will react to the incomming velocity values.
That will mean that changing your controllers velocity curve will change the velocity values send out from your controller when you play the same way as with another curve, and thus also a application will recieve another velocity value that it will react to. Applications will allways react the same if it get send the same velocity value.
So both settings have an impact, but velocity today has values from 0 to 127. Nothing sum up, but you may feel changes, when you change velocity curves on your controller or your application. It's about send and recieved velocity values.
(It's possible to same multiple velocity curves in Piano V3.)