Where are scanner drivers located, and what (file) form do they take?
Scanner drivers are located in /Library/Image Capture/Devices/ as Tetsujin so helpfully points out.

These scanner drivers are App bundles, but quite a bit different than regular applications. An executable binary is inside Contents/MacOS, along with the obligatory plists, Resources, etc. Even so, they're typically quite a bit more barren than an actual Application bundle.

If Tetsujin wants to include an answer here, please upvote his rather than mine since mine is basically just repeating information that I got from him.