When you say that the users are still able to see all devices, I assume that you are referring to a node list they have on the home page.
If you will create a node custom property containing the servers and then use that same CP to create the server group dynamically, you will then be able to limit the node list and the group list to the same set of servers.
Does that help?
I'm saying that this user is able to see all devices. In other words, the account limitation doesn't do anything.
Based on your recommendation, couldn't I just limit the account based on the custom property rather than build the group using the custom property? Either way, shouldn't I be able to simply limit an account based solely on a Group full of nodes?