Well, if "cold hard fact" is what you want....it does depend on who you ask.
I can tell you this much, Springfield is vague about whether or not commercial 308win ammo is ok for use in their M1a rifles, or at least they were vague last I checked. I don't shoot it in mine very often, but during hunting season I have fired a few rounds of Winchester. In general, I myself do avoid using regular 308 because I handload, and have plenty of both match, and hunting ammo.
Now that being said, to the best of my knowledge, the biggest difference between 7.62x51mm and .308win is the thickness of the brass. The military brass is thicker, and will hold less powder. The same can be said for 556mm as opposed to 223rem. In both instances the military cases are (or may be) slightly longer at the neck, thus the commercial brass is shorter. I've found the length difference more often in 556 myself, but I've heard it said that it can be an issue with the 7.62 as well.
So, when I'm working my handloads, I just trim all the cases to the proper length for commercial specs. That takes care of any length problems, and leaves the capacity issues caused by the difference in brass thickness. To deal with that problem, I've reduced my personal powder charges by about 10%, and that has worked just fine for me for at least the last 10 years or so.
The thing is, with the commercial, store bought ammo, you just don't know what's in it. But, with the thinner brass, it will hold quite a bit more powder. I seriously doubt you'll ever have an issue with a M1a blowing up, because of using Win, Rem, etc, but A steady diet of it could cause premature wear issues.
It could be a little hard on your operating rod, locking lugs, roller, etc....
I really hopes this helps answer your question.
An M1a is what I'd consider a modern and durable weapon, and I'm sure it will hold up just fine.
I would worry more about some of the older mil-surp stuff, like the Indian SMLEs chambered for 7.62, and stuff like that.
Please bear in mind, I'm not a "gunsmith", but I've been doing this stuff for many years. So I guess it's better than advice from a internet mall ninja