I can verify that this is true. I was looking for the same thing and Nimsoft support confirmed that it is not currently possible. I am completely awestruck that such a fundamental feature is not only completely missing but that apparently at the time, nobody had even complained about this.
I assume what the OP is trying to do (which is completely logical) is to create a group like "Servers" that ALL accounts will see, and have it filled with all servers at whatever origins that account has access to. This sounds like an incredibly basic requirement but is not possible.
We have 36 separate hubs/origins and about 30 client accounts, the fact that I have to manually go in there and define a "Servers" group (and a network device group, and an applications group, etc) for each account is insane, especially using the terrible GUI (I know it's possible via sql but it's still not something I'm willing to put myself through).
Until this functionality is present I'm not going to show USM to any of our clients.