I just encountered an AI ship with multiple scanners equipped: https://i.imgur.com/3XPKlIg.jpg

Do these things stack? As in, does having multiple scanners increase your chance of discovering caches/etc?

No, they don't stack. If you want, you can remove one of them and replace it with something else.

The initial scouts were all designed with two to make them symmetrical; some of them were implemented as built-in, and some of them were implemented as removable, and we left two on the latter just for cosmetic reasons. I believe it's the Ashdar and Gremak scouts that have twin removable sensors.

Gotcha, thanks!

I kept symmetry by putting the scanner on the weapon slot, and putting weapons on the scanner slots.