No. There are few roaming Pokemon in DPPt, main ones I can think of being Mesprit and Cresselia, which both have Psychic STAB, meaning that they will do substantial damage to Crobat. Mean Look is therefore useless for them.
Nearly no one switches Pokemon in game, so Mean Look is not needed. Go with Fly, Confuse Ray, Pluck/ Aerial Ace and X-Scissor/ U-Turn. Crobat doesn't need a Poison move because it only covers Grass types in Gen IV.
X-Scissor is a more effective counter to Psychic types, or U-Turn if you used the X-Scissor TM on something else.