Hi Blue 1,
Yes it's possible to use a mobile devices hotspot with a Chromecast. But you 'might' need another device with the Google Home app connected with the hotspot to set it up as some mobile devices can't create a hotspot and also connect with the same hotspot.
I haven't heard from you in a while so I'll be locking this thread. Feel free to start a new thread should you have more questions and concerns in the future. We're here to help.