Couple of issues between the appearances of the
Xindi-Insectoid and the
Elysian-Insectoid:
* The Xindi has two prominent antennae. The Elysian does not, appearing to have a smooth forehead.
* The Xindi has two arms and two legs. The Elysian appears to have four arms.
* All Xindi-Insectoids appear green, while the Elysian is brown. This isn't that big of a deal, since most humanoids have pigment differences, but there's no evidence in Enterprise of anything but Green Xindi-Insectoids.
* Xindi Eyes are large, bulbous, compound eyes (modeled after a common fly, I believe), while the Elysian appears to be just a large, yellow slit. This could be a product of animation, simplifying the eye structure. However, we see a compound eyes in an earlier episode (Beyond the Farthest Star) with a race of
ancient insectoids.
The Elysian might be a Xindi-Insectoid, but if that were the case, it would have to be some unseen secondary insectoid species of the Xindi.
I'm 99% certain, though, that the Xendi and Xindi are one and the same, just a product of spelling reform after two centuries of working closely between the two races.