I use my fight gloves for training and everything. Like I use mine on my heavy bag (if you hurt yourself hitting a HB, you're going to hurt yourself punching a person weighing even more). The only problem I've ever had doing this is that my knuckles got a little scrapped up at first, but they callas over really quick. I use them for sparring too (half contact) and they work just fine. I have a pair of everlasts with Japanese katakana on the front, ran me twenty bucks.
The only reson to hit the bag with MMA gloves on is that you are trying to impress someone(yourself methinks). Or you simply cannot afford a pair of bag gloves. With the amount of time you should be spending on the bag you will undoubtedly hurt yourself with those mma gloves. When you fight you should be properly wrapped under the gloves to add protection. Invest in your hands, get bag gloves, and proper wraps.