You can connect any wifi device to a hotspot. The question is whether your carrier will handle the data from any device but the one on your account. (Come carriers do, some charge you extra for tethering, and if you don't pay, the tethered device - the gopro in your case - doesn't get connected to the internet.)
You can't use the hotspot for the wifi connection that the phone is connected to, you need a device with 2 wifi adapters to do that. You can only use the phone's mobile data connection.