For the Darkrai that don't carry Psychic (I assume Dark Void, Dark Pulse, Substitute, Calm Mind) what's stopping someone from carrying a more defensive minded Heracross? A Heracross with Megahorn, Close Combat, Stone Edge and Sleep Talk, or perhaps a previously status'd Heracross like the one used to beat Gliscor could do a lot to keep Darkrai from getting into position. The user of this Heracross could use it as a backup sweeper for whatever strategy s/he might have.
If you want to keep switching your Heracross into STAB Dark Pulses from 135 Base SpAtk while you take residual damage from a potential Burn Orb, Stealth Rock, Spikes, Sand Stream/Snow Warning and Toxic Spikes, be my guest. This is another pokemon: "sure I can do the job, but don't look at me the second time you need a switch-in" argument.