In universe explanation :
Sensates have not yet been proven to be harmless. Perhaps they irradiate some sort of factor that turn other people into sensates as well ? Perhaps they carry a disease that is inoffensive to most (healthy carrier) but might kill some ?
As long as you haven't captured them and studied them you cannot be sure it is safe to be around them.
Out of universe explanation :
Hazmat gear just looks scary. If you want to make scary henchmen but still want them to be related to scientific purpose, the Hazmat gear fits both.
It also brings back memories from SF alien movies where they usually wear this kind of gear to approach aliens. (Emphasize on the abnormal/otherworldly side of the sensates)