[Update: Tested! Crayon works on iPad Pro in iOS 12.2 beta 6. Jason Snell first shared this detail in a Macworld piece earlier this week too.]
According to Nilay Patel at The Verge, Logitech Crayon support is coming soon to the iPad Pro. Nilay says Apple tells him support will be added through software in the next update to iOS 12, presumably iOS 12.2 which is likely due out on Monday.