The Panzer IV is probably the Ausf. H, because god forbid Relic would ever have to design a new model for the early marks.
Honestly they could rip the model from CoH1 if they really wanted to, it differs slightly, different exhaust and some very minor details. Has a weird muzzle though, I think it's just a fictional muzzle whipped up real quick by the modeller, they should probly use the CoH2 version of the gun..
I'm tempted to think that the P4 is just from the Ostheer and it was added in along the same reasoning that the Soviets are in the trailer, to show the integration of everything. Relic would face no end of trouble if it recycled units into a new faction...
I don't see the problem with recycling the Panzer IV. It was the backbone of Germany's armoured forces, you don't have a lot of choice in that department. It'd be like trying to portray the Americans without Shermans, or the Soviets without T-34's. I wouldn't be surprised if OKW had Grenaidiers or Panzergrenadiers, and they're sure to have Pioneers.
I remember when Panzer Elite came out, the endless threads of "Why doesn't PE have Tanks" and "What am I supposed to rally by forces around?"