Is being socially reclusive okay for a graduate student?
Is "OK" good enough?

It's "OK" to be strange and reclusive, but being socially reclusive will stunt your career long term. You will not be considered for projects, not be sought after for collaborations, students who go on to success will not be as likely to reference your papers or publications in informal situations, and you will be less likely to be considered for promotions/tenure/etc. Not maliciously perhaps, but the social recluse just doesn't come to mind as often as more gregarious colleagues do. It essentially closes doors unnecessarily. This isn't to say that you shouldn't be true to your personality, but the fact is that success in any field of endeavor, even academic ones, is as much affected by your social skills as your intellectual skills. 

Look at the mid-nineteenth century physician Dr. Ignaz Semmelweis, who identified that hand-washing and sterilization of instruments drastically reduced incidence of death from childbed fever. Because of his poor social skills (note that he was actively abrasive and confrontational rather than merely reclusive), he was unable to gain acceptance for his findings, and unsanitary medical practices continued despite his efforts.