Hi @abroun_beholder, welcome to the forum 
Apologies for the delay on this - it took some time to get confirmation on the current state of things.
Somewhat, but not entirely. There is an AP_ADC MAVLink message in the ArduPilotMega message set, and it’s even technically supported by ArduPilot firmwares. The caveat is that it’s currently compiled out for most flight controller types (including the Navigator) unless they’re compiled in a debug mode, which in practice means it doesn’t actually get sent.
I spoke with the software team and we agreed that it seems like a valuable feature to have, especially since it’s been asked about before. That said, it’s not an immediate priority for us (since it’s new functionality that’s not strictly required for effective operation and standard use of a vehicle), so I can’t provide a timeline for it.
For what it’s worth there’s an open issue about it that you’re welcome to comment on and/or provide contributions towards if you’d like to help/encourage the feature to get implemented.
As a side note, it may be possible to get access to the ADC readings in the interim via a workaround, whereby you configure an additional battery monitor and set it up with an offset of 0v and a multiplier of 1.
There’s some possibility this could work, but it’s likely preferable to do something else instead, especially since there are other known approaches (as discussed above) that are less likely to cause conflicts.