. Can a well constructed plant table provide the same isolation as an audio rack??

As a general rule most rigid stands and racks don’t isolate. They exacerbate the vibration problem - instead of reducing structureborne vibrations rigid stands and racks amplify them or facilitate their transmission. The trick is to decouple the component from the floor, either by employing the ubiquitous mass-on-spring technique or by employing a wobbly non-rigid structure like the Flexy Stand of yore. The more rigid you try to make the stand or rack the better transmitter of vibration it becomes. Or you can employ a rigid stand or rack and isolate each component on it separately using the mass-on-spring technique.

geoff kait
machina dynamica
isolation is our middle name

A rigid wooden table with low mass that keeps the units still should always work well and look nice.
 
There is also additional question of where the table is sited. Wooden floors are ok as long as the boards aren't too wobbly. 

Concrete/tiles are easier to work with if you want to get and keep the resonant frequency <10Hz. 

As sometimes with benign distortion, some might prefer a modicum of resonance a desirable ingredient to add flavour to their sound!

A plastic called acetal (brand name Delrin) has excellent properties for a shelf. It is strong, easily shaped, and is a very poor transmitter of vibration.

A 1" slab of that under your turntable should work very nicely with any old table. Cost, a few hundred.