wonder about making this in a Vitamix?

The function of the ice cream maker is to chill a liquid mixture until it is mostly frozen. Usually there is a slow-moving dasher to stir the ingredients so they freeze uniformly (to prevent undesirable ice crystals) during the chilling process.

I suppose someone particularly clever could fashion some sort of collared bowl engulfing the Vitamix's blender top with a waterproof gasket that prevents melting ice from dripping into the motor housing and causing a dangerous situation.

An easier workaround would be to simply put the blended ingredients into some sort of receptacle, stick that in the freezer and periodically stir as it chills. The end result would not be as uniform as a something from a dedicated ice cream maker but it might be adequate for your table.

Best of luck.