The Neutral really doesn't come into it.
The potential is there for a ground fault to render the emergency stop non-functional though.
Assume the control wiring is as follows:
Phase -> Start -> Overload -> Local stop -> Coil -> Emergency stop -> Neutral.
Now imagine a ground fault develops on the line between the coil and the E-stop switch. You would never notice it until you came to use the E-stop, because the local stop would still function just fine.
Of course, you could say that putting the E-stop on the "hot" side of the coil also leaves room for a short to phase to do the same thing, but I would have thought that a ground fault would be the more likely.
[This message has been edited by pauluk (edited 02-10-2006).]