Yes, it is possible to manage them, I request you to build a Agent Handler for particular that domain and open all required ports to ePO console. Separate domain machine will get all updates from ePO console through Agent Handler.
That's not really necessary... ePO does not really use domain authentication for the majority of its functions, so if the machines in Domain B can communicate with the ePO server in Domain A, then you should be fine. You simply need to install the agent package from the ePO server on the Domain B machines that you wish to control, and that should be enough. The installation of the agent is the only tricky but, as you'll need credentials that are valid in domain B, but that's it.
Check out the ePO and MA product guides - the various options are pretty well covered. An additional agent handler probably won't be required.
Thanks for the advice. Have successfully added machines from the other domain to ePO and they are now reporting in correctly.