Cisco LMS can be used to monitor both a LAN and a WAN environment.
We run a Cisco LMS server on our main campus which monitors our Cisco equipment on our LAN and across about 10 or so WAN sites.
I think your choice of whether to use your LAN connected LMS server to monitor your WAN connected sites comes down to bandwidth. Monitoring across the WAN will use some of your WAN bandwidth so if a WAN link cannot spare a little bandwidth then it might be best to deploy a remote LMS box.Again, if you have many remote sites as we do, putting a LMS box at each site would be too expensive.
Our WAN sites are connected with everything from 256k serial lines to 2.4Ghz and 5 Ghz wireless and we monitoring them all centrally without bandwidth problems.