I also see APRS messages in my VX=8DR memory dump, so I'm interested in building a more complete memory map for that radio.
I dug much of the APRS beacon bits out of my VX-8DR probably two years ago. I had some very rough python that would dump the received beacons from a raw memory dump, which I think is/was the same as a chirp image.
The messages and message headers are storied separately. I didn't figure out how the radio sorts them to figure display order and which memory to reuse next.
Ideally I'll find a way to get APRS messages from the radio to the computer in real time (perhaps an undocumented command in clone mode), however enumerating commands for Yaesu radios looks a bit dangerous (CAT command sets seem to include full reset, which even resets factory tuning parameters).
I never came across any whiff of any sort of CAT support or any other serial control beside clone mode for the VX-8DR other than clone mode.
I did discover that the radio will keep receiving and processing APRS messages while in clone mode, and you could initiate as many transfers as you wanted while in clone mode to get the most recent messages.
Even so, that's a more APRS-centric thing, not really something that would go into chirp.
I thought it would be helpful to be able dump out the list of received beacons, from chirp especially for objects such as repeaters, but I never got around to doing anything with it.
I'd dig up my old stuff.
--Rob