In the Avengers movie, Dr. Banner is discovered treating patients for some unspecified, possibly unknown, disease in what looks to be the slums of India. From my recollection, Banner is a gamma physicist and not a medical doctor (Ph. D not M.D.). While it can be argued that the Indians may or may not know the difference, Banner hardly seems the type to con people for a quick buck.
From the Bruce Banner Wiki entry " Bruce Banner
Banner is considered one of the greatest scientific minds on Earth, possessing "a mind so brilliant it cannot be measured on any known intelligence test." He holds expertise in biology, chemistry, engineering, physiology, and nuclear physics."
So basically he has one degree mentioned on the marvel site but he actually has studied beyond that but apparently didn't receive a doctorate in any other field.
The TV version of Banner was definitely a physician. http://en.wikipedia.org/wiki/The_Incredible_Hulk_(TV_series)#Premise
I don't remember the comic books mentioning a medical degree.
In the movies, he's a physicist rather than an M.D.
Update - in Thor: Rgnarok, he mentions having 7 PHD degrees in one scene. It’d be strange for him to not mention an MD at that point, if he did have one.
In the comics before after completing his undergraduates at Desert State University in Navapo New Mexico he went to medical school. He started dating Angela Lipscombe while he was there. In their final semester Angela got a research grant for her neuro-psychiatric research but Bruce could find no one interested in his medical applications of gamma rays. He left abruptly presumably without officially graduating. He also studied at Harvard and Pennsylvania State University.
It was after this, that Bruce went to the California Institute of technology and gained his doctorate in physics and applied his interest in Gamma to weapons tech. most of Bruce's medical training is revealed as back story when He encounters Angela in later comics. Incredible Hulk Vol. 2 Issues 12 through 20 are good examples. So in cannon he has MD level medical training.
He was a polymath so it is quite possible that he had medical knowledge without having a formal MD.
He was not necessarily conning anyone, merely helping out where he could.
The short answer would be no, he's not specifically an MD.
Does that make him a con artist though?
Through all the different writers interpretation of the Hulk story, Banner is a genius physicist and has worked with biologists specializing in human gamma ray exposure. It's quite likely that a genius could pick up a lot of the skills needed to act as a doctor in a third world country.
He also needs to hide since he's being hunted and not work as a genius physicist, so he definitely would need to be able to "con" people to be able to hide effectively.
So it just follows the story line for most marvel superheros. A lot of them do have to hide their true identity making them seem that much more "human" than the "white knight" type hero's of other stories.
He isn't called Dr. Banner by accident.
As a child Bruce was withdrawn, possibly developing a split personality to help deal with his pain and rage. His only happiness came from spending time with his cousin Jennifer Walters. Bruce found it hard to develop friendships and often found himself on the receiving end of physical abuse at the hands of school bullies. One such incident sparked him to build and plant a bomb in the basement of his school. The bomb was a dud, and Bruce was expelled, but the military took notice of his genius. Eventually, Bruce earned a doctorate in nuclear physics and started a career with them.
He spends years in hiding, probably studying with hands on training in 3rd world countries. Not as though he can attend an accredited Medical University and Degree without popping up on the grid for General Ross to find him, right? He's a super genius, 7 years in the jungle with Doctors without Boarders is likely better than half the "50/50-flip-a-coin", "Common-causes-only", "one-issue-at-a-time" crock-pot doctors you get at a normal clinic. And I have a plenty of doctor friends!