If introduced properly...most IPO dogs will bite something other than a sleeve. You can basically trick them into doing it and once they do it once, realize its okay, they'll keep doing it.
The reasons its not done were listed by hunter...
I work in SDA and in IPO, and you realize dogs will bite whatever you train them to bite. They'll also have their favorite spots...which is what you tell an SDA helper before you trial, so that they know what to present to the dog for a bite. So even on a coat...my dog bites the forearm.
And everytime I see that in SDA it makes me cringe. There isn't much padding in a suit sleeve. I have scars on my bicep from suit bites. There is no way on earth I'm taking a forearm bite in my suit. Folks don't realize how hard a dog can bite, just the pressure... My male's grand sire was notorious for breaking forearms on the street ... I train mine to target bicep/armpit from the front, or tricep from the rear... so for the OP, you can see a dog can be trained "if sleeve present, bite sleeve. If jacket, bite armpit." etc. A helper failed to get a pillow out quickly with Katya and took a thigh bite from her in scratch pants... and we've never done a single leg bite... so some dogs, are getting their bite come **** or high water.
Hunter, CWDC UScA Helper
Beschützer des Jägers v.d. Sportwaffen
Katya v. Hügelblick
SG Aska v. Ketscher Wald
Yōkai v.d. Sportwaffen
Arya v. Allrothaus