In my experience when there is any major issue going from an old prior firmware to the newest, Nuvyyo has things it up so that your unit upgrades in stages, from that Tablo’s installed firmware X to interim firmware Y (not necessarily the one immediately following X but the right incremental step in their coders’ views) and then to current firmware Z. I don’t think this needs to be worried about.
The only issue in an arcane way that I can think of might be that since you can “rollback” only to the last installed firmware, if you are on, say, 2.2.26 and the Tablo does choose to first install 2.2.28 before 2.2.30 (rather than jumping straight to 2.2.30 if the coders have determined that will work fine), any rollback would be to 2.2.28 rather than the long-experienced 2.2.26.