LMS is primarily for a LAN, but you can discover remote routers depending on how far away they are (timeouts) and the protocols you are running. For example, if you are discovering across an ATM link you would need to make sure that ILMI is configured properly.

LMS depends on SNMP and CDP to discover its devices and this would have to be enabled and make sure there are not timeouts along the way.

Also, if there are pix firewalls along the way you won't be able to do a cdp discovery.