Yes, you can do this. You'll need to first make sure you are using the correct All Nodes Tree (I like the All Nodes Tree - Ajax resource).
Second, use the custom property editor to create two custom properties: "Loc" and "TypeOfDevice" would be two great suggestions ("Location" and "DeviceType" are already used in the database and populated by the SNMP discovery). Once you build these two properties for your nodes, populate them appropriately.
When you finish with that, go back to the Orion web UI and edit the All Nodes Tree resource and you will see that you will have 3 categories. If you follow the above suggestions for names of the custom properties, you would define the categories as being broken out in the following order: "Loc" / "TypeOfDevice" / "None". When you are through, apply the changes to the resource and you should see the results you want.