If a pilot has the capability and a positive attitude, then they ought to be given a fair crack at the whip.
I vaugely remember someone telling me that historically, a very large percentage of pilots who leave Logan within the first couple of years of working for the company are from south of 55ºN. Hence the reluctance to employ from outside the Porridge Curtain.
I could be wildly off the mark on that one, so don't shoot me down on it. Two of the previous posters are evidence it isn't a blanket ban anyway.