One of the settings you can set for Supervised devices is the ability to block modifying the Hotspot settings. However, AFAIK, this does not remove the setting; it just disables it (greys it out).
Are you saying that the Hotspot setting isn't even showing up on your devices?
Do you have any configuration profiles you're applying to these devices? Have you checked them to see if you have inadvertently pushed a setting in one of them that may be doing this?
I checked the settings and Hotspot is not blocked. If that was the case all the devices would have the same issue. It's just there, I've contacted Sprint and reset network settings and still not working. The option for hotspot is just not even there.
Do you have the ability to reset the phone entirely? If so, does it happen after a reset? Is there any commonality between the iPhoneOS on devices that show the hotspot, or devices the don't show the hotspot option?