Hi,
Did you install other instances of NSX on others vCenter servers ?
Are you able to see them from your vSphere web client ? If not, did you enable vCenter enhanced linked mode (not mandatory to work with Cross-VC NSX) ?
If yes, you have to declare the first one as "primary node" and other as "Secondary node".
You can check the lab HOL-SDC-1625 out on hol.vmware.com, it is very interesting and provide a good guidance about working with NSX over cross vcenter environment...
You should also take a look at the NSX 6.2 installation guide VMware NSX 6.2 for vSphere Documentation Center