There are a few reasons that flag is not an option. The most notable being that the current representation of what is commonly called "The Green Mountain Boys" flag is almost certainly not historically accurate. In fact, as many know, there is no intact surviving example of this flag. The remains of that flag that we do have, are housed at the museum in Bennington Vermont. Though the image at right is a poor one, when viewed in person what is noted is that the flag appears to be only the remains of a canton of a much larger flag with what appears to be tattered green silk on three sides. Though the color has been disputed, some assert that what appears to be green silk is in fact black silk faded with age, the fact remains, the current representation is a fanciful assumption.
What is known is the flag was carried by General John Stark, commander of the New Hampshire forces who fought and were successful at the Battle of Bennington, which was not even fought in Vermont, but that's another matter. There is no historical evidence to suggest that Stark commanded any of the actual Green Mountain Boys led by the Allen brothers. This all asserts the fact that there is no historical evidence that this flag had any connection to Vermont at all. The fact is that the flag is reputed to have been handed down through the Stark family and that pieces were cut off and given as souvenirs over the years til all that remained is the canton. As far as what that flag actually looked like in it's entirety, that is still a matter of debate.
The flag's canton shown below bears a striking resemblance to the Stark fragment which leads many to believe that the Stark fragment is in fact one of the Gostelowe Return flags. An adequate description of them is given here: http://www.11thpa.org/unit_flag.html
The heart of it is quoted here: "Among the papers of the Continental Congress at the National Archives is an extensive inventory or “return” of arms and other military stores on hand for the months of July and August 1778 at Philadelphia and outlying stores and repair locations. The Return was prepared by Philadelphia Major Jonathan Gostelowe, one of the Commissaries of Military Stores for Lt. Col. Benjamin Flower, Commissary General of Military stores for the Continental Army. A separate section of the report is titled “A Retrun of ye New Standards and Division Colours for ye Army of ye United States of America In the Possession of Major Jonathan Gostelowe, Com’y Mil’y Stores.” The report lists 13 Standards (Colors/Flags) that were in his possession at the time of the report."
The only one of the Gostelowe Return flags listed in the above mentioned document that was described as having a green field was the first one listed, called The Headman Color and described as bearing "a pillow on top of which is the cap of liberty supported by thirteen hands" and whose motto was "This we will defend or Die." The remaining fragment shown below left along with the modern representation shows how much artistic liberty is given to modern representations of historic flags.
Could it be that the canton housed in Bennington is actually a missing piece of the above left remains?
All of the historical evidence does not shine a very favorable light on this flag as far as it's connection to Vermont is concerned. In the link section of this website, there is a much better article written by Dave Martucci, of which the above is based, which will help everyone understand, that this flag has more ties, in fact, to New Hampshire than anywhere else.