Americans shouldn't be afforded any undue niceties, the principle of having a home/away system holds strong enough in the Nations cup where it is about optimising fairness, but even though WNL isn't obtuse enough to have the word 'European' in its titled it fairly obviously is a European Tournament. Call me a reactionary but I don't see a reason to offer them a fair footing in European Tournaments when they go to the lengths that they do to restrict Europeans reasonably playing in their main tournaments - Why should they share in the fruits of our competition when they protectively shun our players from their community?
With that being said, I don't think that it's reasonable to have a blanket ban on American teams but they should play on German servers in the unlikely event that they sign up.