Sorry, when I said two gateways I didn't mean two actual installations. mabye the screenshot below will clarify.
You say DM Gateway can talk with agents in different networks, mabye I have done something wrong, but that dosen't seem to happen. As the screen below shows, one gateway is active (10.8.128.x) and will pick up agents from that network, but not from 10.8.129.x if I need to contact agents in that network, I will need to disable gateway and activate the other one.