You provided a limited information about your ADDM architecture. Hence, I assume you have a standalone appliance. Starting v8.3 ADDM appliance maintain a Proxy Pool where you can add multiple Proxies. In your case you may get AD proxy deployed in each datacenter and make both of them belong to the same Proxy Pool.
I further assume there is no Firewall between your DC's. If this is not the case you need to consider Firewall rule that allows traffic between AD Proxy(s) and appliance (tcp/4321).
All should work well in your case.
kouznetz is absolutely correct.. I only want to add that you may want to view a few community tutorials to help guide you through the setup and configuration. So have a look at this blog post here where I describe the tutorials to view if you're interested in configuring ADDM for windows discovery.