Yes, this is very common in beer brewing and wine making - filling up headspace in primary fermenters with glass marbles.
I don't like the idea as I don't need a 14th thing to carefully sanitize. Instead, I just displace the headspace with CO2 and have had good success with that.
This is not at all common in beer brewing. I cannot speak for the wine world but most of them have variable height lids.
No brewery would ever put glass marbles into a primary fermenter. As a professional brewer we routinely try to have the beer touch as few items as possible, post chill, due to sanitation risks. Not only would marbles be a nightmare to sanitize (tiny chips or cracks would not be properly sanitized), its a logistical nightmare to later get them out to clean the tank. Tanks are cleaned in place with a pump and spray ball method without ever opening the tank. Getting excessive hops out is enough work much less marbles.
Breweries purge any air out of a tank with Co2 before filling, for multiple reasons, but since Co2 is heavier than air it will settle on top of the unfermented wort as it is gently transferred into the fermentation tank thus removing the need for any kind of marbles or headspace reduction.
A second major reason this would not be done is that when beer ferments it needs extra headspace as the yeast in an ale ferments on top of the beer. A hefeweizen will routinely create a yeast layer about 10-15% of the height on top of the liquid. So if this space was blocked it would be forced out the top, which for most modern breweries would create a large mess into the floor drains and lead to the yeast count being too low reuse.
On the flip side I would be very interested to know of a brewery doing this and why.
Air and surfaces are filled with random mould spores and bacteria. If they touch your beverage (which is by definition full of stuff that mould loves, because yeast is a mould) then they will grow, causing off-flavours or even poisons. You prevent this by sanitising everything, and making sure that any headspace is filled with either carbon dioxide or sulphur dioxide. CO2 is produced naturally by fermentation and because it's heavier than air it settles in the headspace displacing oxygen (moulds need oxygen to reproduce). Sulphur dioxide can be added using sterilising tablets (Campden tablets). Other techniques are to reduce the headspace by adding more liquid, or marbles, apparently, and using an airlock to stop air entering.
There is nothing that can grow during fermentation in beer or wine that will hurt you. It will just taste terrible, or unplanned.
In lower abv fermentation such as kombucha or fermented vegetables. Molds can be a risk if the starting medium is not low enough ph, or high enough salinity.
Something like aspergillus flavus could poison you, although you'd notice that because it would be clearly visible as a green mould with a terrible smell & taste. I homebrew myself and agree that poisoning from ordinary brewing (not distillation) is incredibly unlikely.
They work abolutely amazing for me, if you leave it for a while the wine often tastes much better. The vacuum appears to produce a special kind of decanting. (Technically, it's more like 0.5 atmospheres)
the ones like Eto work because they displace air which is necessary for the bacteria to turn the alcohol to vinegar. Well actually slow it down. I can confirm the Eto works okay and wine keeps pretty well for a week or so. and yeah I did a side by side with a couple of $10 wines of the same variety after two weeks one was nasty and the other was still drinkable and not gone completely off by then.
I don't like the idea as I don't need a 14th thing to carefully sanitize. Instead, I just displace the headspace with CO2 and have had good success with that.