Yes, they all can, as they learn Dutch proper only at school (and Frisian, for the Town Frisian speakers). But they have a certain pride of their languages, especially the Zealandic speakers, and I am pretty sure I can get some willing contributors behind a Wikipedia. (I won't even request it if my quest for other contributors fails!) Wouter
Same with Cashubians in Poland - the goal of Cashubian Wikipedia is mostly preserving the language.