Starting with Adaxes 2015 it is possible to configure allowed Exchange forests and servers for Adaxes: https://www.adaxes.com/help/AllowedExchangeForestsServers.
Currently, there is no functionality to do what you want.
Also, when Adaxes tries to find available Exchange servers, it first tries to connect to all Exchange servers, starting from the servers located in the same AD site where Adaxes is installed. Once Adaxes finds an available Exchange server, it starts performing all operations on that server. So, the errors will appear only at the stage of finding available Exchange servers.