Legion Speer (later merged with Legion Todt) was indeed part of the NSKK. Dutchmen joined in, though most of them were forced: Being transported to Deventer (eastern Netherlands) and/or Berlin and then to a SPeer-unit. NSKK Speer (as I like to call it) was active allover Europe. I found a handfull Dutchmen operating in Finland and Norway, a few in Yugoslavia and a few of tem in Poland. French, Flemish, Danes, Russians (though as Hiwi I guess), Walloons and Estonians served in NSKK Speer.
I must add NSKK Speer was never a full part of the original NSKK. Korpsführer Kraus never had any authority over it, Willi Nagel (a personal friend of Albert Speer) was in charge.
Always in need for info about: Dutchmen in the NSKK, HJ and TeNo.