I have found a few discussions about this in forums, but being one of the people who works closely with the MM team and not being able to find an official ruling, I thought it better to come here for official clarification.
So the information I have compiled.
On page 138 of TW, the description for ATMs talks about how ATMs have two other ammo loads and function similar to other specialty ammunition without directly calling them specialty ammunition.
On page 238 of TW, there is the block about Aerospace units not being able to use Specialty Munitions with a few added exceptions.
On page 304 of TW, the two alternate ammo types for ATMs have the weird triple dollar symbol. This goes down to a note blurb at the bottom that has rules for ATMs from both Non-Bay and Bay weapon attacks [this also lines up with the table in TM showing the alternate ammo types of ATMs having an aero damage calculation]
With the above information I have one question, and just a general expansion on said question for clarity sake.
Can ASF utilize HE or ER ATM ammo?
And then
Can the other Aero type utilize HE or ER ATM ammo?
If this question had been answered before I apologize [especially if the answer is a relatively easy one]. I could not find an answer in my searches. I even poked the MM team to see if they knew.