My mistake. It appears that rail mines and poisonous spider spawners (like the one mentioned in the description) are not generated. However, there are still other types of structures in the mines.
Steps to Reproduce:
Create a new creative mode world with "seed" 1
Make sure the "generated structures" option is off in "world" settings
Go to position 74 : -14 : 10
Observed Results:
There is a generated structure with a spawner
Expected Results:
I would not expect to see any generated structures in the mine
Here is a link demonstrating the issue in vanilla Minecraft, with corroboration.
https://www.youtube.com/shorts/CgW3dGngdJ4