Ashlanders worship their ancestors' spirits, right? So if when you die your spirit becomes a "blank slate" in the DreamSleeve, then how can anybody possibly worship your spirit when it's been wiped away in the dreamsleeve? I don't see how that can work.
Ah, so it's not like Ashlanders
see their spirits and commune with them or anything. It's kinda like how here on earth, people pray to God or Buddha or whoever without actually physically seeing or having a conversation with him. So Ashlanders simply do their ritual stuff and just assume that their ancestors can hear them or are acknowledging their praise even though they're not because once you die, your specific personality and spirit are no longer in existence.
No, the Ashlanders do see their spirits and commune with them, they even talk with them (see http://www.imperial-library.info/mwbooks/ancestor.shtml).
"The departed spirits of the Dunmeri, and perhaps those of all races, persist after death... The bond between the living family members and immortal ancestors is partly blood, partly ritual, partly volitional. A member brought into the House through marriage binds himself through ritual and oath into the clan, and gains communication and benefits from the clan's ancestors...
Each residence has a family shrine. In poorer homes... This shrine is called the Waiting Door, and represents the door to Oblivion.
It is a family's most solemn duty to make sure their ancestor's remains are interred properly in a City of the Dead such as Necrom. Here the spirits draw comfort from one another against the chill of the mortal world... These remains become a beacon and focus for ancestral spirits, and for the spirit of the remains in particular. "http://www.imperial-library.info/mwbooks/ancestor.shtml
Its quite possible that the Dunmer religion has managed to circumvent the dreamsleeve process to some degree through the bonds of ritual, oath, choice, the power of myth, and internment either in Necrom, an ancestral tomb or a burial cavern. In accordance with
"reappropriation of spirit towards its aligned AE" the Dunmer spirits enter into this ancestral bond. Spirits can be forced to remain in the world, the spiritual bonds of their religion seems to have accomplished this as the norm for the Dunmer race.
Granted:
"Recently dead spirits know us well, and do not quickly forget their living kin; they are weak, but quick to guide and protect us." That ancestors know the world better immediately after their death might imply that even in their ancestor state they are subject to the dreamsleeve erasure, or this might just be the natural effect of being less connected to the world.