Yes, neuro lit crit is legitimate to the humanities, because we can understand English better when we understand how literature affects our brain. It is a field that is in its infancy, but it shows great promise. If we can understand how literature affects the hard wiring in our brain, we can understand ourselves, as well as the literature better.
The 'neuro lit crit' is legitimate to the humanities. If it was not legitimate to the humanities, then people would not be interested in it at all. People who think that the 'neuro lit crit' is not legitimate to the humanities are just being close minded and are not open to new things.
The theory of neuro lit crit or where they combine neuroscience and cognitive science into literary theory is a new direction for the humanities. There are a lot of interesting possibilities that could come from the new way of thinking. Humanities, like most other subjects, benefit form new ideas and new perspectives.
I just might think that it may be a legitimate approach in some form or another and should not be ruled out so abruptly as so many might rather it but instead allow it some time to be examined more closely but until then, I would have to put my money on yes.
I do not believe 'neuro lit crit' is fully legitimate to the humanities, or maybe better put, it's not going to make the field boom, as some would like it to. The fact is, is that humanities, and especially literature are niche subjects, especially in today's world where people want there information handed to them in small digestible bundles.