I'll stick my neck out and say that they are polypropolene and yes they may well be wilton, I would never take the customers word for it as YOU are supposed to be the professional although it may have a label on the backing to say what it is.
First do a burn test to see what the construction is of the face fibre, the backing which is the wilton part should be woven not cloth backing, to clean safely and hopefullt foll proof I would vac very well front and back, apply MS to face fibres and bonnet clean, if you want to dabble then a quick HWE and turbo dry.
If it is what I think it is then they are prone to shrinkage but definately cleanable with great results providing you identify first.
Shaun