Keep in mind that Western Union is very common for remittance payments (workers sending money home from other countries) so it might be a universal payment system that they are used to working with down there.

Last time I used Western Union via a cc was in the 90's and there was something like a 3% fee. I'd take cash down to the local store with a Western Union and do that.

Western Union is used by scammers because you can transfer money to anyone anywhere in the world so basic common sense should be used, make sure it is a real company with real reviews, etc.. Don't do anything Western Union related with online forms/Craigs List.

Also I don't know for sure, but yes I'd guess it would be treated as a cash advance