You can change their account limitations to only display objects in their group.
2) Manage Accounts
3) Select the Account/AD User(s)/AD Group
4) Press "Edit" button
5) Under Account Limitations - Click the "Create Limitation" button
6) Select "Specific Group"
7) Choose whichever group you want them to access
One caveat is that you want to make sure that you remove mention of any other group or devices they don't have access to or they'll constantly get System Errors if they click on inaccessible devices/nodes and it will make your life miserable. I personally like to do group limitations while also creating specific views and menu bars so that they're locked down to only their area and then there's no confusion among departments. I hate getting complaints about errors, so that's an easy one to avoid. Let me know if you need some clearer steps or help with creating views. It can get tricky and most of that list above was off the top of my head so some button names may be incorrect.