Has anyone setup a GE 750 relay to provide protection against unbalanced faults using the negative sequence element? I have been told the recommended setting for the relay would be 50% of Phase TOC pickup with other settings remaining the same. Is this a good assumption?

I would run a unbalance fault analysis on the circuit in question first. Unbalanced fault current is tough to determine and relies on zero sequence component values in cables, buses, etc. as well as the fault return path impedances. 50% sounds more like a factory setting to me.

I found this paper in IEEE's database that explains how to coordinate the negative sequence elements. Its called Negative Sequence Overcurrent Element Application and Coordination in Distribution Protection written by Elneweihi, Schweitzer and Feltis.
Per the paper, |3I[SIZE="1"]2[/size]/Ip| = Sqrt(3). I can figure out the pickup based on this equation and other coordination requirements described in the paper.