The default for IP Office (since 4.0 if I recall correctly) for unanswered calls is to use the mailbox of the original call target regardless of subsequent forwarding and other options, i.e. the first user or hunt group to which the call is targeted.
So in your scenario the call will end up in the hunt group mailbox.
That applies to all the voicemail server options. However as amriddle implies, Voicemail Pro has the flexibility to allow you to override that if required and to put messages into the mailbox of the last extension number to which they are presented.
Their is a long technical tip on how to do that if required though I can find which one it was at the moment.