the deep ones might be The Dwemmer
No they are not.
- They are not because the Dwemer are all extinct.
- They are not because the Dwemer are not Lovecraftian.
- They are not because the Dwemer did not live under Hackdirt.
- They are not because nobody can decipher what the Dwemer wrote, so the Brethren couldn't have understood anything from a Dwemer book.
- They are not because I said so above already.
- They are not because the depth of the Deep Folk is spiritual and intellectual, while the human name for them is "dwarves", not "deep ones".
- They are not because it would be really dumb.
- They are not because I have a two-in-one torch-&-pitchfork combo.