This is a known issue. In PM, it is possible to add the same device, to many IP domains, but in Spectrum, we can only add it to one.
Error When Adding Device to IP Domain
I tried to add a device to a CA Performance Center IP domain in OneClick. I received an error message that stated, "The following models could not be added to the Global Collection Domain Name." An additional statement claimed that the models did not exist. But I have verified that the models do exist in the landscape.
You see this message if you attempt to add a device that is already associated with an existing IP domain to another IP domain. This error can occur if, for example, the device was added to the IP domain either manually or dynamically, using a Global Collection rule. The portion of the error message stating that "The model does not exist" is inaccurate. We plan to address this issue in a future version of the CA Spectrum software.