As far as I can see, ingame models don't really support the notion of Mer having slit pupils, but as we all know, any ingame representation of characters is too often a case of "gameplay!=lore" (Oblivion, anyone? then there's the case of Dunmer losing their original uniformly glowing eyes over the course of the series...).
So, from the lore-friendly point of view, would it be completely wrong to assume slit pupils were at least characteristic of the Chimer, or maybe even common among the general "purer" strains (Aldmeri - Altmer - Chimer and Dwemer)? Bosmer would most likely have round pupils since they "soiled Time's line by taking Mannish wives"...