I just learned glass embedding was a thing so excuse the potentially stupid question.

Also, would it even be worth it in terms of potential accuracy increase?

Most people call it glass bedding.
Isn't that stock made completely of plastic? If so, it probably isn't rigid enough for the bedding to make any difference.

M1a does not lend itself to free float the barrel due to the gas system that hangs from it.  It is intended to be mounted in a stock with a certain amount of tension on the front band.  Optimally you want to unitize the gas cylinder to the front band.  They have free floated double lugged receivers.

Glass bedding could be hit or miss with the material that the stock is made out of.  If it is nylon or polyamide based, the bedding compound doesn't like to stick to that material.  You would have to bed it in a manner to get a mechanical lock into the stock for the bedding.

Typically a fiberglass resin type stock takes the bedding compound perfectly.

Glass bedding an M1A is the exact opposite of free floating.  Due to the design of the rifle, you want to lock everything down so that the action doesnt shift within the stock between shots, and that is done by locking the front down with the barrel band (unitized gas sys) to the forend and by bedding the receiver to the stock.

Generally speaking, the ProMag stocks hold very tightly, and bedding isnt necessary.  There again, you would need to inlet the stock to accommodate the bedding compound (epoxy), and there isnt really enough stock material there to be hogging out without compromising stock integrity.