Well - Dilophosaurus' crest is represented in it's fossilized skull. And the Dilophosaurus' neck frill and ability to spit venom (black goo) is part of established JP movie canon, So it is perfectly acceptable for the game to portray Dilophosaurus as having a neck frill and give it the ability to spit venom.
This game is based on JP lore so they can do basically anything they want to the Dinosaurs. Just cause it isn't represented in bone doesn't mean it's not there. Maybe it wasn't a bony crest.