Dark Command is treated as a spell, but is no longer subject to hit chance. It can't be cast when silenced but no longer has a 17% chance to miss raid bosses (in contrast to the 8% chance to miss boss mobs for melee attacks). Prior to Patch 4.0.1 even if you were melee hit capped (263 hit rating at level 80), Dark Command's chance to miss is still 9%. This 9% gap can was mostly covered with Glyph of Dark Command (removed in 4.0.1).