It's not the same hardware, the Nanostation has two Ethernet ports and the UAP only has one. In both cases though I think the AR7241 internal switch is involved. (this is because the bootloader recovery expects to TFTP from what would be a "LAN" port on a 5 port router, not the separate un-switched WAN port). So even though only one of the five PHYs on the AR7241 is actually wired out to a physical port, it is one of the switched ones.
For snapshot builds consider the "LAN enumeration" note from the Nanostation page:
These should still be swconfig based. Is the swconfig command present? Does it show the switch port going up and down as the network cable is plugged and unplugged (on the other side of the POE injector of course).