->The term cultivar is an abbreviation for a "cultivated variety".  A variety is below the sub-species level, thus a cultivar can not be a "highly complex mix of many species".  Daylillies are typically clonally propagated correct?  If so, they are not true cultivars, although they would commonly be referred to as such.  To technically be a cultivar it must be a cultivated breeding population that exhibit characteristics that allow them to be distinguished from the other members of that species.  

 -> Any hybrid within a species is an intra-specific hybrid.  IMO the cross between two daylilly cultivars would not be a hybrid at all unless they were, as I mentioned before, inbred lines.  However, it could be considered an FX (whatever generation it is) interspecific hybrid of the original species if you do not consider them as species in their own right.