About non vocaloid covers: yes they may be added. It's recommended to add a note at the position where it says "Notes". Layout: # "Songtitle" {{nnd|nndid}} (Translation) (Notes) -XXX ver.- feat. [[Singer1]], [[Singer2]] and [[Singer3]] (YYYY.MM.DD) (note that most of the other parts of this layout it optional), specifying what kind of song it is (in that case write Kemono Friends OP)
Afaik, ETA is just a live tour, and we don't add live tour covers to the List of covered songs, since it wouldn't be complete ever.
Instrumentals shouldn't be added, as this is utaite wiki and we focus on the singing aspect. But you may mention it in his description (if very prominent e.g. if he's trying to become a producer or if he does a lot of those instrumentals) or in his trivia (if it's just a few tracks now and then).