SQL Sentry supports the monitoring of clusters and only needs to know the virtual name of the clustered SQL Server instance.
SQL Sentry can also run on a cluster. You can install the SQL Sentry Monitoring Service on one or both nodes of a Windows cluster. If it's installed on both nodes you will have full fault tolerance, and if one SQL Sentry Monitoring Service goes down, the other one will pickup the load. SQL Sentry doesn't use Windows clustering, we use our own clustering technology, so you don't need to use Cluster Administrator to configure anything. Simply point both SQL Sentry Servers to the SQL Sentry database during installation, and SQL Sentry clustering will auto-configure itself.
It's important to understand that our clustering isn't at all dependent on Windows clustering, and two or more SQL Sentry Servers can be installed anywhere in the environment with the same effect...in the scenario above we are just leveraging the two cluster machines for this purpose.
Please also see SQL Sentry's System Architecture.