Unless you have devices which are not connected to the network most of the time, have credential issue or just want usage data you would be better served using agent-less discovery especially in a data center environment.
A single UD agent can be discovered by multiple UD application servers. You need to make sure you have the same UD certs available in all CMS systems. Currently there is no way to copy a cert from one server to other.
The workaround is to export the domain credentials via JMX console and import them to CMS server where you need same UD certs. Then you can use copy function available domain manager to move the credential from a copied domain to new one.
Actually the use case was to have several machines in Dev and Test pointed to our Dev/Prod instances pr iTest/Prod instances by using multiple agent the idea was that we could upgrade(patch) the agents per policy promoting them through the environments for I.T. while retaining full inventory/asset information for the business.
As it works out we'll just have to move some nodes back into Dev & Test then upgrade/patch them there and then be able to ge tapprovals to move the upgrade/patch into production.