Probably not. Mobs will be 33 or higher so taking a lvl 31 into the raid will be like taking a lvl 28 in to VoG hard. Maybe 1 but damage penalty will make them all but dead weight. Plus why aren't you 32 by the time hard mode comes out? Loot drops have been fixed somewhat and normal will have been out for 5+ weeks before hard drops. With all the Crota cheeses and with the ability to solo the entire raid you should probably be 32 by the time hard mode drops. Personally I will probably only allow a lvl 31 in my raid team if it is a clan member who is looking to raid with an alt.