Hello Sean
If you use the command ip ssm default, as in the lesson, then the 232.0.0.0/8 range is used by default. Alternatively, you can use the ip ssm range ACL_NAME where the the ACL_NAME is the name of the access list that defines the multicast address range you want to define. This way, you can use a range different from 232.0.0.0/8. In both cases, if you try to join a group outside of the specified range (either default, or otherwise specified) it will be dropped.
No, the router will not know you want to use SSM simply the the range being used. You must use the ip pim ssm command.
IGMPv3 is necessary for SSM to function, and all participating routed ports must have IGMPv3 enabled.
Yes, it is possible to use this range just like any other multicast group if you do not enable SSM. You can find some more info about SSM at this Cisco documentation:
I hope this has been helpful!
Laz