Can I use ZOTAC mini PC as a workstation?

It would depend on the applications that you are using the workstation for. Whilst applications like CAD/CAM which require heavy load number crunching would do better with workstation GPU, ZOTAC have mini PCs with discrete high performance Nvidia Geforce GPU like GTX1060/GTX1070/GTX1080 which would be ideal for graphics design/video editing.