Ok, So today I was bookmarking the sections in my rulebook and came across the section on deep striking. I read over the section a couple of times and something occurred to me. If I'm reading the deep strike section correctly, then the only requirement for it to occur is that the rule has to activate (read Deathmarks ability to deep strike during the enemies turn.) The only reference to the way it occurs in the rulebook is that a unit must be in reserve and make a reserve roll. The rest of the rules refer to the turn that the models arrive as the turn. For example, movement mentions "In the movement phase in which they arrive" and shooting says "In that turn's Shooting phase."
So "IF" I am reading this correctly then the deathmark's deep strike ability happens at the same time as the enemies reserve, so you actually interrupt their turn to make a deep strike and a shooting attack / running during their shooting phase. Of course then things creep up like when do they get to shoot / run.
As I mentioned, I may be reading this wrong. So if you guys wouldn't mind giving the rule section a read (pg 95), and see if I'm just crazy.