Watch out for unanticipated disk shelf firmware upgrades. We now make a point of deliberately doing the firmware at a time of our choosing.
I can't remember the exact chain of events but it went something like this, after doing an OnTap upgrade, a new version of disk firmware was available on the system. The disk shelves started upgrading themselves (all at once!), a process that takes a reasonably time and certainly wasn't convenient when it occurred.
So our schedule is RLM first, the Disks and lastly OnTap itself. So far this seems to have worked for us quite well.
I am not sure what the consequences would be from letting firmware lag but I have always felt it best practice to keep upto date if we can. I know others though who have an "if it ain't broke don't fix it" policy.