¿Cisco IOS NAT admite traducciones entrantes en una interfaz Frame Relay?? ¿Admite traducciones salientes en el lado de Ethernet??

Sí. Encapsulation does not matter for NAT. NAT can be done where there is an IP address on an interface and the interface is NAT inside or NAT outside. There must be an inside and an outside for NAT to function. If you use NVI, there must be at least one NAT enabled interface. See How do I configure NAT?for more details.