On the CNC shield V3 the enable pin is tied HIGH so that the steppers are disabled by default. One must enable the steppers in code. Set the pinMode of Uno pin 8 to OUTPUT and digitalWrite pin 8 to LOW to enable the steppers.
Yes it is. I have 3 CNC shields on Unos and populated with the DRV8825 drivers that work just fine. Just plug the drivers into their respective headers making sure that they are oriented properly and set the coil current limits and they should work just fine. Set the microstepping jumpers before plugging in the drivers.