The ScrollWheel tracker included with the vizconnect library returns Z position data. This could be combined with the X and Y data returned from the viz.mouse.getPosition() function:
Code:
import viz
import vizact
viz.go()
from vizconnect.util.virtual_trackers import ScrollWheel
mouseTracker = ScrollWheel(scaleVelocityWithDistance=True, extensionAccel=100, debug=False)
def printData():
print mouseTracker.getPosition()
vizact.ontimer(1,printData)