For both Oracle Linux 5.8 and 6.3 . I did complied HP driver on rhel base kernel and add it on kickstart.cfg file along the OS installation. And I change the default grub to boot as rhel base kernel.
What if I reboot the server to UEK kernel. Do installed HP drivers on redhat base kernel will also work or compatible on UEK kernel?
Do I need to re-compile the drivers and install again when booting with UEK kernel?
Yes, you need to recompile the drivers for each kernel you wish to use. Each kernel version has its own specific kernel module directory. You can check /lib/modules. Drivers you install for one version of the kernel are not used by another. The same applies to the initramfs boot image. Driver installations usually fail if the running kernel is not recognized, but it depends on the type of installation, for instance, source or binary.