There be a difference between them, according to the strange creatures we affectionately call tryndees.
Nevaeh is indeed "
Heaven" spelled backwards; Neveah ("Haeven" spelled backwards) supposedly has the aforementioned "butterfly" meaning.
To "confirm" the above, just check such sites as Babynames.com or Babynamesworld.com.
Miranda
Proud adopter of 15 punctuation marks; see my profile for their names.