There are a couple of things you can do to monitor the license server. First, you can monitor the service on the license server. Second, the license server uses port 27000. You can monitor that port by telnet-ting to it and see if you get a connection. There are many software packages on the Internet that will monitor services and ports.
However, I have found that my license server was originally unstable and crashed all the time. We requested a new license file from VMWare and everything has been working just fine since.
Specifically, the license file that we had originally received from VMWare came in two pieces (we added additional licenses). Although VMWare has instructions for merging the two files, the license server for some reason just didnt like it. So once we got one complete file, the license server has been stable.