German attempts to raise an American Waffen-SS unit from POWs only drew enough volunteers to outfit a single platoon. A handful of Americans also served in the "Legion of St. George," a similar attempt to create a British/Commonwealth Waffen-SS unit.
Many of the volunteers for these units were simply interested in easier duties or getting out of a prison camp, although there were definitely dedicated converts among them. It's very difficult, given the murky motivations of these volunteers, to judge just how dedicated they were - especially since very few of these volunteers actually fought for the Germans in combat. Most served as translators, recruiters, and in other non-combat roles. Some British and American volunteers did join larger Waffen-SS units.