I know this gallery has a handful of legit futanari (e.g., pages 36 and 37), so both tags are valid, but the vast majority are shemales and should be recognized as such. Even the artist gets it wrong (e.g., page 20).
Also, be aware of the crossdressing (e.g., 72) and gender bending (e.g., page 316).
EDIT: As usual, voting me down is easier than proving me wrong. I don't know why I expect more. I guess it's my boundless faith in humanity…