Isolation for tube amps

You are correct. You really can't protect from 'airborne' vibrations. However there is a lot of other equipment or room floor induced vibrations which can be audible by thier effect on the signal, especially tubes and phono playback. So proper isolation is important. And you can eliminate most of the airborne vibrations by using the volume control. :-)

Would the HALO tube dampers help with airborne vibrations?

Galen Carol Audio in San Antonio,TX sells inexpensive tube damping rings for small preamp tubes which I've found to be quite effective. I don't know of anything available for power tubes though.

"Herbie's Audio Lab" sells several models of very effective tube dampers for most sizes of tubes.

Don't underestimate the ability of a well designed isolation base - like the Silent Running Audio bases - to deal with airborne vibrations. The SRA isolation bases literally attenuate airborne vibration by converting the energy to heat. In my experience, there is no product that is as effective as an SRA iso base in dealing with the vibration problems inherent in an amplifier sitting on the floor - especially a tube amp, which tends to be more sensitive to vibration than a solid state amp.