Not having ever used Linux on a Mac such as this one, I've no idea if the video input is supported but a quick google suggests it isn't - that is, I can find plenty of information that in older documents (contemporary with the hardware) that it isn't, but nothing newer that it is not. It's not listed on the hardware compatibility list of Yellow Dog, which I think is the most Mac-friendly of them all?

I did not assume that this was possible. Apple most likely never released any specs since they did not assume anyone would be interested in such information...