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If you grind oily dark roasts, the oils stick around in your grinder and go rancid. That's what you're probably smelling. You just need to clean your grinder some what regularly. This isn't a problem for medium-lighter roasts and water added with RDT doesn't really have any effect in practice.

Hendon, the head of this research, stated that the humidity in the grinder went as high as 70% iirc but the humidity would dissipate within a matter of seconds.

It may matter for some grinders but he stated no concerns.

The coffee will no doubt soak up any small spritz of water quickly, it's basically a desiccant. No chance mold will be able to use that water.

If you do this you would clean out your grinder more often I presume