Q: How do powers such as Killing Spree, Infernal Wrath, and Stormhawk's Vengeance interact with instant kill effects?

A: Many Fourthcore Team Deathmatch powers are of the instant death variety. Telefragging, E1M1's Meat Grinder, E3M1's Pit of Wombs, etc. instantly kill an enemy. Most of the powers in question trigger on a character going to 0 hit points or fewer. Since the instant-kill terrain powers do not change the target's hit points, the other powers do not trigger.
In other words, no Killing Spree for telefrags.