OES 11 SP1 upgrade to ....

I'm running OES 11 SP1 over SLES 11 SP1 (workgroup, with Groupwise on the same server) and it's time to upgrade it (it's never too late).
I'm asking if is possible to skip some SPs. For example can I upgrade directly to OES 11 SP3?
Does SLES must follow OES or I can upgrade SLES and OES separatelly?

Thanks for help,