In fact, it's an Dilgar ship as the designers of the Sierra B5 computer game envisioned it. But that game was scrapped before it was completed, so this design for a Dilgar ship was never released, which made it something best classified as "work in progress" at that time.
However, while the guys at Sierra were thinking about Dilgar ships, the Guys at AoG were doing the same.
And they did manage to get their -quite differently looking- designs approved by Babylonian Productions and Warner Brothers, released in their supplements and as miniatures! Again, see the pictures on AoG's last stock list.
So, even though some fan CGI artist (and one of the better ones) made the Sierra design into a mesh, it actually isn't too likely to exist as Dilgar design in any kind of halfway canon B5 universe - those universes should use the "green clamps of death" style ships (as they of course did a whole fleet and not only a single cruiser design) AoG thought up (which Mongoose cannot use yet, as all the AoG stuff hasn't found it's way into their hands so far - either legal problems or they simply haven't managed to get it yet).
So, that's it.
Personally I much prefer the AoG designs, even though I do have a weak spot for the Sierra color sceme (Hmmm, gold-brown with black markings...).