Yes it is true, although not quite well stated. I think what Matt meant, and certainly what it true, is that the MEK in Polyfiber will not work with some components of Stewarts. While it might not dissolve a cured top coat, for example if one were to apply Polybrush over fabric that had been glued with Stewarts, you would certainly have problems. That is what I meant when I said "unless you know what you are doing..." I know of at least one certificated aircraft manufacturer that uses Stewarts glue (actually just the 3M product) and uses DuPont products over it through top coat- so it can be done.
To the OP- I see you are in Illinois. I'm in Wisconsin- Milwaukee specifically, and I'm painting an aircraft with Stewarts right now if you want to visit and see it in action. PM me for contact info.