Hersh does have a reputation as a serious journalist and his reports do need to be considered seriously. However he is also a particularly controversial journalist. For example he does seem prone to using anonymous sources which it may be argued are of low validity or may even appear to be made up.
I'm inclined to feel "one swallow doesn't make a summer". If other journalists, and commentators with some level of credibility, do come out and support Hersh, then maybe we will feel he is the one that has broken this important story. However right now I'm not at all sure this story is credible. I think Hersh's own (complex) response to his Jewish roots has to be considered.
All Hersh has managed to do is raise the possibility that Obama may have lied - which leaves open the opposite view that he did not lie. At the moment it is a non story.