Regardless of weather sealing lenses will get dusty if they breathe. If any outside lenses move the internal volume of air must change and that means air is being exchanged with the outside.
Do they at least have filtered air vents? Most hard disks (the non-helium-filled ones) are very carefully sealed except for a single vent that has a big filter on it.
Dust in a lens isn't a big problem. It really doesn't effect the image quality [1]. They had another tear-down to remove a fly from Canon 70-200mm [2], and it didn't make difference until stopped down.
I don't think that necessarily implies that the inside will get dusty. For example, if the air intake had a HEPA filter with a sufficient lifetime, only particles smaller than the filter's rating would be able to enter the body of the lens.
First, hepa filters tend to block flow of air A LOT. Lens designers strive to get lenses to focus as quickly as possible. Any blockage of air would necessarily make it very difficult for the lens to breathe quickly.
If there was no exchange it would create a pressure differential. I don't know how large it would be or if it'd matter though, but if it weren't large enough to overpower the mechanism or make it difficult to use, it could avoid purposely exchanging air.
This lens, same as (for example) the SELP18105G (E-mount APS C 18-105mm/f4 Power Zoom) is fixed-length, meaning there is nothing moving on the outside.
If the lens does not breathe there would be no advantage (it can just be airtight without being vacuum) and if the lens breathes (ie changes internal volume) it means the motor would have to work against atmospheric pressure which would be extremely difficult in a lens to do reliably.
Counter question: Why not fill lenses with Nitrogen? I know outdoor cameras CCTV cameras do this (more so to prevent condensation from internal moisture).
You'd still have to compress the nitrogen going one way to zoom, and pull the nitrogen against air pressure going the other way. Focus motors powerful enough to do that, plus including movable airtight seals to keep the nitrogen inside, would make the lens a serious chunk bigger, heavier and more expensive.
The dust that gets inside from breathing while zooming rarely affects image quality to any meaningful degree. Excessive humidity can lead to fungus growing on the glass though, which really can ruin your contrast. It's normally good enough to keep your lenses in a box with some silica desiccant during summer to prevent that.
It's pretty hard to make a vacuum with moving parts included in the wall of the chamber. The better your vacuum seal, the harder it'll be to move the lens elements and vice versa.
And if the seal fails then you'll get a lot of dust inside.
