Slowclimber may or may not be talking about Hurn. regardless, that's exactly how it's done there. Grasscutter moves out of strip for any aircraft the controller asks him to,usually large jets etc. The topic has been raised many times with management and S.R.G. over the years and no-one has ever expressly forbidden it. Seems to me that it will only be judged to be illegal following an incident involving the tractor/aircraft etc. If you happen to be the controller on duty, god help you.