When a computer boots the first thing that happens is the computers bios activates the hardware.
Yes hot plugging is in Puppy Linux, but it is not perfect.
Especially if you are hooking up a USB controller (which a USB hub is)
How exactly is the computer identifying the hub to Puppy, when it is plugged in????
The computers USB controller is involved in this.
The hub is going to hook multiple USB devices into the computer, all by one computer USB port.
who knows, maybe this hub actually needs specific Linux kernel hardware support.
So maybe the kernel being used, by the Puppy version, is a factor.
Hardware support is the biggest reason to use a newer Linux kernel.
The rest of your questions are affected by, what specific version of Puppy, when it was developed, and how Puppy worked at the time it was developed.
Some of the latest versions of Puppy, that have the latest changes on how Puppy works, are suppose to support removing the Puppy USB drive, and now be able to use that USB port, for some other drive.
Fossapup64 9.5 is not one of them.
However the save file/folder does have to be on some other drive, so it is still available to use.
That is another recent change for booting from a Puppy on a USB.
Allowing the save to be placed on another drive.
Up until recently and the newest Puppy versions.
The save had to be placed on the USB drive the Puppy install was booting from.
I have not really tried doing this, because I use Puppy from a USB SSD drive that is always hooked up.
I think BookwormPup64, maybe F96-CE, probably the newer versions of Vanilla Dpup, etc..........would be good for you to try to do what you want.
Any Puppy version that was built, using the fairly recent version of Woof-CE.