Upgrading IBM x3650 M3 7945-AC1 From ESXi 4.1U3 Embedded to ESXi 5.5U1 Embedded --- 5.x Embedded Not on Compatibility Chart, But 5.x Installable Is

We have an IBM x3650 M3 7945-AC1 [Intel Xeon E5507], and are currently running ESXi embedded 4.1, build 1363503 :

~ # esxcfg-info -e

boot type: visor-usb

~ #

esxcfg-info --system | grep -i "version 4\.1"

         |----Version...............................................Version 4.1, Build: 1363503, Interface: ddi_9_1 Built on: Oct  8 2013

While aware that there is new patch released for 4.1 this month, we'd like to upgrade to ESXi 5.5.

The compatibility guide for the IBM x3650 M3 [55xx] shows the latest supported version of ESXi embedded being 4.1U3, but the latest supported version of ESXi being 5.5U1 :

How is one supposed to upgrade to ESXi on an embedded installation? Why is "ESXi" supported on version 5.x, whereas "ESXi Installable" and "ESXi Embedded" aren't?

A similar compatibility guide chart of IBM BladeCenter HS22 blades as hosts shows the same versions for ESXi embedded, however we happen to know of an existing HS22 blade running ESXi embedded version 5.1 that was upgraded from ESXi embedded v4.x. Is that therefore an unsupported configuration? How was it possible for that system to be upgraded from 4.x? What are the implications for our x3650 M3?