I haven't seen the 501 first hand yet, but from my understanding the switch ports are standard unmanaged ports with no routing capability built in. You would need routing functionality to have IP addresses from different subnets on each of the ports. So, yes all IP address would have to be in the same subnet.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...