As welding can be of various voltages, frequencies, ac or dc, and of any polarity- with these often being switchable settings on the machine- I do not think that the table should in any way be deliberately connected to the building's electrical system.
This is especially important as "power quality" issues become more important.
Experience has shown no need to go in the opposite direction; that is, isolating the table from the structure with insulators, etc.
At the heart of the welder is a transformer. This is a "separately derived" source. Any connection with the building's system should be through the transformer.
Ground rods are useful for voltage stabilisation for the power company, and lightning protection for you. Neither reason applies to welding.
