Do the Xeon CPU's have unlocked Multipliers ? or are they locked?
If they are locked does anyone know Why?
Server parts value stability and reliability over overclockability. Also no server component provider would support overclocking as it introduces only new possible problems rather than benefits.
also, is it harder to make a CPU with an Unlocked Multi vs a Locked one?
It should be the same as making any other cpu, aside from the bits that lock the multiplier. The manufacturer however needs to validate that it runs at all the multipliers properly which may take more time than a locked multi.
Also, what is the reason for making some CPU's Halogen free?
These are mostly environmental protection reasons, see ROHS. A few micrograms per processor of a toxic substance quickly adds up to a few metric tons when you are producing thousands of chips a day.