I guess that will come down to the numbers and I don't know those I'm afraid. The fact that the valves run hot won't help (I believe solids tend to become more permeable as their temperature rises). Any micro-cracking around e.g. glass-to-metal seals would be a particular problem. And most people are surprised to see how thin the glass envelope of a valve is, usually the first time they break one.
All that said, I wouldn't expect occasional exposure to small amounts of helium to bother a valve at all. Hot filament ion gauges are made of glass after all
https://www.lesker.com/newweb/gauges...m#Hot_Filament. Operating a valve day and night in a high-pressure helium atmosphere might be a very different thing though. But at least we would only have to worry about ion current and eventual gas breakdown. Helium is extremely unreactive and I wouldn't expect it to chemically poison cathodes the way air or moisture or many other gases can.
Cheers,
GJ