I had a conversation with a Senior Advisor on Apple Support Live Chat today. The short answer is: it's not possible via USB.
TRANSCRIPT EXTRACT:
Me: I was just wondering if there is a way to copy photos and videos from an iPad which is supervised to a computer (not the computer that supervises the device) via a USB cable?
Me: I have done lots of Googling and searching of the Community Forums, but I have not been able to find an official apple response.
Me: If you look at this link, you can see lots of people on the Community Forums have the same problem [link to Community search results for "supervised ipad photos"].
Apple Senior Advisor: Ahh, wow, this can be a difficult one. Essentially, iOS devices setup with a profile using Apple Configurator can only be used completely with the computer they were setup with. For importing photos, syncing, and other concerns this can make using them physically with a computer difficult.
Me: I realise that a supervised iPad cannot synchronise with another computer, but I cannot find if it is possible to just copy photos and videos.
Me: Is there a way to copy photos from a supervised iPad?
Apple Senior Advisor: It will not interface with any other computer by USB, except the one it was configured on originally. This includes importing Photos and Videos.
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Apple Senior Advisor: The Profile used on it would have to be removed for full access through USB, with other computers.