!!! What, no way.
A simple module that contains just 'Transfer' action will take place so quick that in Monitor's Voicemail status screen it isn't even shown. But that's more to do with how often Monitor updates, the module still uses a port license even if only for a few milliseconds.
Just tested it on a 4-port licensed VMPro. Busied out all four ports with users doing mailbox access and then tried to make a fifth call, a short code to the aforesaid simple transfer callflow. No joy.
Callflow routing using things like "CLI Routing", "Route by Call Status", "Route Incoming Call" and "Transfer" actions with no prompts are quick enough to only use the VMPro for a few milliseconds but they still need an available licensed port in order to work. Slightly different from saying "only audio sessions are licensed".