For Oracle Linux 6, Update 4 OS, you can append the PXE label directly to the driver disk. However, for Oracle Linux 5, Update 9, you need to manually make a customer driver disk.
In this example, you are appending Red Hat-based driver disk (2.6.32-358.el6) with base OS initrd.
Label OEL6u4-LX507 Kernel OEL6u4-vmlinuz append initrd=OEL6u4-initrd.img,OEL6u4-xsigo-rhdd-2.6.32-358.el6.x86_64-5.0.7.LX-x86_64.img network