Dilophosaurus is at least referenced in the movie. Some extras saw a graphic on set illustrating them. And like Frenchfries said, the Lego set suggests we might actually see them - probably fully grown, in an attack scenario.
The main reason we've assumed they're not in is because they're not referenced on the website's species list, but that can be explained if Dilophosaurus isn't a caged exhibit (which makes sense as they're explaining the venom, spitting, frill and head shape on bad DNA).
Also, the list is probably incomplete. There's
another species list based on a prop within the film, which has some animals that aren't on the website - including Spinosaurus (which we know is in the film at least as a skeleton, in its pre-2014 form) and Plesiosaurus, which some sources have indicated to be inhabiting the lagoon. It appears to show Dilophosaurus, as the Alien Queen-looking silhouette in the middle of the left half.
