First off, DON'T run unequal versions of IP Office and Voicemail Pro - get your VMPro on R11 to match the control unit.
The IPO has a 3.5mm jack on the back for an external music on hold source, you can use anything that has a 600-ohm output, be it a radio, CD player, mp3 player, streaming service, or dedicated player for MOH content.
You can also upload wav files to the system, and you can program analog station ports as additional external MOH sources.
In your hunt group programming you can select an alternate MOH source if you want something different from the regular system moh, and since you specifically asked about hunt groups, you can also add announcements through VMPro interspersed with the MOH stream
Define what you want, and I'm sure you'll get advice