I will investigate if future versions of the Awesome Miner Remote Service can be used to forward the connections to other miners, like your Antminers, on the same remote network
Has this ever been implemented?
I'm getting a few antminers on a remote network where I don't have control of the router so I can't port forward.
Otherwise, can I install the manager on a machine in that remote network and still use the manager in the local network? Would the local one be able to use the data that it gets from the remote manager?
It's not implemented because VPN is often a better solution when you connect to multiple miners on a remote site.
Although you can connect multiple Awesome Miner applications to the same Antminers, you cannot connect one Awesome Miner instance to another Awesome Miner.
It sounds like you are allowed to install software on the remote site, so my recommendation is to install VPN software in this scenario.