A truckmount user in Cumbria cleaned half of one of his regular pub jobs with a Thermodry bonnet system and the other half with his truck and was gobsmacked to find the bonnet cleaned side looked much better.
He hadn't disturbed any of the deep down dirt with the bonnets and had only cleaned the top of the pile. As it dried very quick there was no wickback of dirt from the base of the pile.
The truckmount side, although removing vast amounts of dirt did still leave some there which wicked up casuing a slight dulling effect.
So yes it can be done but it is not a thorough a clean as HWE. Best would be to do what Arenaclean suggests and extract and post bonnet.