Is Research Fellow a gender-neutral term?
Yes, in your reference, the third definition is the one being used, rather than the first:

a member of a group of people who have shared interests, activities, etc.

Of course, we should look to how the word is actually used rather than solely to its dictionary definition, but in this case I think that actually makes the argument even stronger, since academics use the neutral form quite a lot and nobody else (at least in my part of the world) seems to care for the word.