Are Kurenai's eyes some sort of Doujutsu?
Actually they are not ke-ke-genkai. In this wiki at the latter part said that:


  Although her eyes are very distinct, they are not a dōjutsu.


Dōjutsu (瞳術; English TV "Visual Jutsu"; Literally meaning "Eye Techniques") are genetic ninja abilities that utilise the eyes, granting the wielder ocular abilities. Being a by-product of specific kekkei genkai, dōjutsu are not classified as one of the major jutsu types.