Hi Peter,
VMDirectPath I/O capability mainly depends on Intel VT-d technology and its support on server CPU/Chipset...
I wish I could tell you better news but unfortunately for some reason even IBM x3100 M4 isn't listed as compatible with VMware VMDirectPath I/O ...
See VMware HCL for details:
VMware Compatibility Guide: System Search
Can you verify CPU installed and chipset used in your IBM server?