I mentioned this in another thread about this same issue. I always ask for 1g and have never had a problem being accepted until a few days ago. So, if something changed in the last few days and NPC villages will no longer accept anyone who asks for ANY gold, why wouldn't the developers tell us? Unless they want these villages to have no defenders. Sure, they have a record of not telling us when things change, so I guess I wouldn't put it past them, but this is kind of a big deal. I suppose it could be a bug, in which case probably the best way to get their attention is to have a lot of people abuse it unfortunately.
I will try to sign up for 0g the next time I can make it to one of these sieges but I doubt it will help since I have been accepted to defend NPC villages when asking for gold in the past.