252 SpA Darkrai Dark Pulse vs. 248 HP / 252+ SpD Kyogre: 76-91 (18.85 - 22.58%) -- possible 6HKO
Bad Dreams: 1/8 = 12.5%
Stealth Rock: 1/8 = 12.5%
12.5% + 12.5% + 18% = 43%
So your SpDef Ogre can't possibly hope to take any less than 43% trying to come in on Darkrai. Seeing as it can't rest anymore not only is it going to be nothing more than a short term answer to Darkrai (it can only come in once more after the initial sleep) but it also can't be used to handle any other special threat. (I suppose you could allow Darkrai to cripple your Choice Scarf user as well but then it becomes unreliable for revenge killing and it isn't going to last any longer than a SpDef Ogre. Plus, Sub spam til a wake up trolls any Sleep Talk choice user.)
Bad Dreams: 1/8 = 12.5%
Stealth Rock: 1/8 = 12.5%
12.5% + 12.5% + 18% = 43%
So your SpDef Ogre can't possibly hope to take any less than 43% trying to come in on Darkrai. Seeing as it can't rest anymore not only is it going to be nothing more than a short term answer to Darkrai (it can only come in once more after the initial sleep) but it also can't be used to handle any other special threat. (I suppose you could allow Darkrai to cripple your Choice Scarf user as well but then it becomes unreliable for revenge killing and it isn't going to last any longer than a SpDef Ogre. Plus, Sub spam til a wake up trolls any Sleep Talk choice user.)