The developer of Radeon-Profile GUI is working on implementing GPU Utilization reporting based on fixes in the latest Linux Kernel.
See the following post for more details on Github: GPU Utilization not displayed on R9 FuryX/Nano. · Issue #92 · marazmista/radeon-profile · GitHub
I also need a Linux ( Debian / Ubuntu) GUI for my R9 280 to check and perhaps change frequency and voltage. The main reason I chose an AMD graphic card is that I heard AMD drivers were open source so it was more supportive of linux users. But if there is not actually the functionality, i.e. a GUI, to support Linux users my next GPU upgrade will be from the Green the team.