He might not "be" a shooting guard (I didn't say he was) - but he guards them, frequently. Those data from 82games are great and valuable, but they don't answer this question.
Not sure what you define as "with regularity". I've never seen him matched up with SG except during some oddball switch. I'm guessing you're referring to fairly short stretches of time. But then again, we've had Rondo on LeBron for shorts stretches of time. I still maintain Crowder can't be counted on to play and/or guard SGs with regularity.
I gave you six or seven examples. Those were not on switches.
"Shooting Guard" - what a quaint term in today's world. But long before we were hearing about Swings or whatever, it was common practice to have two interchangeable wings. Crowder takes the biggest scoring threat - like Harden or Butler or Hayward - or a wing facilitator like Iguodala or Tyler Johnson. He's the Celtics' Wing Stopper. Some of those might be described as "shooting guards", like Butler or Harden, and others might be described as "small forwards"; many teams nowadays play interchangeable wings (like Chicago and Utah last season).
Not sure what you define as "with regularity".
I'll nitpick a little bit here. I said "frequently", not "with regularity". Both terms are not precise, but I would not have said "with regularity". Perhaps you take them to mean the same thing.
Crowder is very capable of defending all but the quickest shooting guards in the NBA. No, it's not ideal, but he moves his feet well, and will have a size advantage most nights. Hayward can then defend the small forward.
I've seen him beaten off the dribble more times than I could count last season. Also, he's 6'6 in shoes, so his size advantage would not be all that great -- except against the 6'3 breed of SGs that will run circles around him.
His size advantage is that he's 235 with a firm base and strong lower body. He also has long quick arms that he uses to get deflections - but now we're getting into his team defense, which is excellent.