In lieu of making an application cluster aware is it possible to set up a trigger based on an event appearing in the system event log to cause the server cluster to failover?
There is a wmi provider for MS failover clusters. Look at the MoveToNewNode method of MSCluster_ResourceGroup. That should get you what you want. You didn't mention what os, but in server 2008 you can easily attach a script to a specific event. Server 2003 should be fairly easy to read the event log and find what you're looking for.
One option would be to use a "Generic Script" resource type. This option is only available on Server 2003 and newer. The basic premise is that you create a VBScript file that launches and monitors the application. As the cluster makes various calls to the script for the status of the application, the script can be told to look wherever you need it to for the information.