You ain't going to be getting any summons in Zul'Aman...:

We had to disable summoning yesterday via emergency hotfix due to some exploits. We're hoping to re-enable summoning as soon as possible. We know it's a big inconvenience and we apologize.

On a related note, we're looking into fixing some issues with summoning that would once again enable us to allow warlocks to summon people into an instance from anywhere in the world. This could happen as soon as the next big content patch (2.4.0) if all of the technical issues can be resolved by then.

People have been complaining that Zul'Aman gear lacks in defense... however Blizzard have responded why:

While defense affects crits and not crushing blows, the tanking gear in Zul'aman provides more options for players. For example if you have enough defense already, there are items where you can get more shield block value or hit rating or stamina which should improve your overall tanking statistics.