VRTSweb is used for the Cluster web GUI.
If you did not setup a Web console in the ClusterService Service Group, it should be fine to disable the service.
Info about this agent from the Budled Agent Reference Guide:
The VRTSWebApp agent brings Veritas Web applications online, takes them offline, and monitors their status. The application is a Java Web application conforming to the Servlet Specification 2.2 and runs inside of the Java Web server, which is installed as a part of the VRTSweb package. This agent is used to monitor the Web Consoles of various Symantec products, such as VCS and VVR.