Was pretty sure they already did but wasnt sure on the details so had to go looking.
Telstra Tracker is gps (and other sensor) based, and player speeds are often reported off the back of that data.
Found this article from just before Magic Round - check out who they mention had the quickest recorded speed amongst halfbacks and backrowers...
Raiders fullback Kaeo Weekes has emerged as the fastest man in the NRL this year as the sport's speedsters prepare to put on a show throughout Magic Round.
www.nrl.com