1) Why can't you call any servitors while ghosted? This seems really tough. I've been eating a lot of deaths (some from my own servitors) and a few back to back because I can't protect myself until I'm no longer a ghost. What do you do to prepare for unghosting as a conjurer?

If you are good aligned, you can request stuff. As a non-good aligned conjurer, I usually scrounge around places ghosts are allowed where you can grab some stuff off the ground to sell. Your options are pretty limited though. Can't really provide any input as to the why, I assume that the imms feel it is a game balance issue.

2) Is there a way to get elementals to take hits for you? The familiar seems really weak compared to the elemental, but the elemental can't start combat.

Elementals with an area elem attack can initiation combat for example air elementals get the airblast command. They aren't very good tanks though, so this is often a way to quickly lose your elemental. The other way to get them to tank is to flee, wait for the mob to redirect to the elemental and return before the elemental follows you. Timing here can be pretty tricky so it's usually not worth it though.

3) Why do you lose all XP when your servitors kill you? Seems like it should be similar to a PK death and you just lose con.

Unbound, they are mobs, and deaths to them are treated the same as any mob death, again, as a non-imm, I can't provide the reasoning behind that, it just is what it is

4) How do servitors react to you getting attacked? Is there a way to get them to rescue or attack a specific target?

They will auto-attack, how quickly depends on their morale. The only servitor that will rescue is the angel, and that is not something that you can command, it just choses to do so based on morale, alignment, and other factors (assuming you allow it too)