Typically DS2246 have IOM6 modules, where the DS4243 have IOM3 modules as denoted by last number.
Again typically shelf firmware goes off without issue and is done as a background process. Two issues, rarely encountered, I have seen have been IOM does not upgrade (stays on previous FW) or upgrade freezes (requiring a IOM re-seat or replacement). On either open a case and have a FE come out to re-seat the IOM if you don't fee conferrable doing it yourself, then if issue persists replace the IOM.
Disks failing to upgrade firmware in my experience is even less likely than shelf firmware upgrades.
If you have concerns, which is why you posted this question, open a support case before you start your upgrades with all the information about your system and what you are doing. So if you do hit an issue you can escalate the case through chat or 800 number, without wasting time waiting for case to be generated then assigned.