Doesn't really need treating any differently cleaning-wise, you should attempt not to get the filling wet whatever you're cleaning
Feathers take longer to dry than foam, and might smell a bit funny whilst damp, that's the only difference I can think of although I'm sure one of the old guard may be able to add something to that
I should think with the drimaster and truck you won't have any problems.
One thing to check though is that the cushions should be properly lined. Someone will have to fill in the blanks here but I think it should be some sort of fabric with a waxy inner, to stop the feathers from poking through.
Might be calico, or it might be that they then need an additional calico lining on the outside of the wax one. My friendly local upholsterer has moved to France the inconsiderate git, otherwise I'd have given him a quick ring to straighten that up.
The bottom line is that these linings only have a shelf life of a certain number of years, so if they're knackered the feathers will be starting to poke through. You need to just inform the customer of this and mention that there may be a few feathers poking through after cleaning, you'll make your nest attempts to minimise this but can't guarantee it not to happen.