If you want to install the Document Viewer Agent (DVA) along with the POA, it can participate in the cluster by failing over along with the POA and its post office. Follow the instructions in Section 22.4, Creating a New Post Office in a Windows Cluster.
However, clustering is not necessary in order to provide high availability for the DVA, because the DVA does not require the database access that is required by the MTA and POA. As an alternative to clustering the DVA, you can install the DVA on multiple servers outside the cluster, as described in Scaling Your DVA Installation
in Document Viewer Agent
in the GroupWise 2012 Administration Guide.