If you install and configure the OWA Extensions on the active node first, running the Enterprise Vault OWA configuration wizard will do the following:
Register forms for the OWA Extensions against the Exchange Virtual Server mailbox and public information stores.
Create in Active Directory the following Exchange Server virtual directories for the back-end Exchange Virtual Server:
Create the following IIS virtual directories on the active node computer:
Populate the Proxy bypass list on the active node computer from the file, Enterprise Vault\OWA\EVServers.txt.
If you examine the log file, Enterprise Vault\OWA\BackEnd200nSetup.wsf.log, after the configuration wizard has run, you will see the lines detailing the mailbox and public folder forms registration.