In the game, several people talk about the Sixth House contracting smugglers. And indeed, in some smuggler caves we do see ash statues and crates of ash statues, and we can assume that those people work for the Sixth House. However, I thought that it's not enough.

This mod adds new NPCs (male and female versions of "Dreamer Smugglers") into those smuggler caves that have ash statues or crates of ash statues inside. I thought that it would be a nice touch if Dagoth Ur sent some of his people to actually oversee the operation of the hired smuggler bands. They have everything that  you would expect from any other Dreamer in the game. (Corprusmeat in the inventory, edgy dialogue etc.) They do not respawn, and 1-3 of them have been put into each cave. There are altogether 18 Dreamer Smugglers for you to hunt down, distributed in 10 different caves.

In addition, when you kill Dagoth Gares, there will be a note in Ilunibi, Soul's Rattle, which provides you a backstory about the relationship between the Sixth House and the smuggler bands, as well as a list of all the locations with directions, so you may prolong your Main Quest by doing a non-journal quest of finding these caves, and killing the smugglers, in order to lessen Dagoth Ur's influence. Or you may ignore my suggestion to hunt them down systematically, and just enjoy the new immersive detail, that you might find Sixth House representatives in some smuggler caves, where the gang works for the Sixth House.

List of smuggler caves to where Dreamer Smugglers have been added:

Ahinipalit
Ansi
Ashinabi
Masseranit
Nammu
Nund
Odirnamat
Pinsun
Punsabanit
Zanabi

I didn't put Dreamer Smugglers to three smuggler locations with Sixth House statues/Crates with Sixth House statues intentionally:

Velfred's ship - You might want to keep him alive for the Hlaalu quest
Hlaalu Ancestral Vaults in Vivec - You might want to keep the gang there alive for the Morag Tong quest
Andasreth - Plays a crucial role in my mod, Liberate Morrowind - Chapter I, and they are not smugglers in my headcanon, but a group of rebels

The note still mentions these locations, (with a different backstory included than being regular smugglers working for the Sixth House) so you may go there and kill the vanilla NPCs there too, if you insist. If you plan to join the Morag Tong/House Hlaalu, or play my above-mentioned mod, you have been warned about the possible problems that killing the NPCs there may cause.

The mod is clean (see proof among the pictures) bug-free, and should be compatible with everything, as the caves modified are rarely used by any mods - but even if they are used in some fringe cases, my mod literally just adds a couple of new NPCs there, so it should be fine.

Thank you, Melchior Dahrk, for the idea of this mod!