Nothing ever is impossible. It is not impossible that the Emperor took regular Baths in the lava of Red Mountain. It's not impossible that a Dwemer TV crew is currently shooting a documentary about us while on the moon. So mere non-exclusion doesn't mean anything.
The idea that the Tseasci worship Daedra relies on the assumption that the Tseasci think like we do. Going by the http://www.imperial-library.info/obscure_text/tsaesci.shtml this doesn't appear to be case at all. As such nothing much can be said about the Tseasci. They remain appropriately alien.
I've never thought about whether the Tsaesci worship, or even acknowledge the Daedra before. But I don't think their beliefs are totally alien. Several of the themes in "And we at it to become it," have parallels in the 36 lessons. These include the notion of a primordeal Dreugh empire, the Wheel as a striking serpent, and the eating/food motif - as in "No word is true until it is eaten."
I don't see any reason to suppose the Tsaesci worship Daedra - but that's because we just don't have any information in that regard. However, there appears to be some deep connection between Tsaesci belief and the doctrine of the Tribunal Temple, at least; and then it's also tempting to compare the Tsaesci with the http://www.imperial-library.info/mwbooks/monomyth.shtml#Yokudan. Perhaps it would be fruitful to investigation the possibility of the Tsaesci being the source of a primeval mythos which some of the contemporary belief systems evolved out of or in response to.