It is not vorlon, but meant to look ancient. The similarity is due to the design criteria of the B5 computer graphics. As a rule of thumb, species on an equal footing with humans have ships with a metallic look. See for instance the markab transporter below or the babylon five station itself.
Ancient races in a league above humans, such as the vorlons, shadows and the beings from thirdspace, are all depicted with ships that look more biological, perhaps reminiscent of an octopus or a spider. It is also stated explicitly that vorlon ships are "alive".
When we then see a bio-like ship of unknown origin, we are meant to conclude that it has been produced by a powerful, ancient, mysterious and likely vanished species.
Asking Kosh ruins several mysteries. Both the ship of unknown origin and the Kosh character represents the unknown and mysterious in the B5 universe. While scifi set in the present day can use aliens to represent the vast unknown, dark and mysterious of the world, akin to how sea-monsters were used in earlier prose or forest-dwelling creatures in even older stories, it doesn't work at B5. Aliens are "mundane" on B5, so you need special mystery-aliens to set up the border between the known and unknown, the border between farmland and the wild forest.
If Kosh takes an active part in studying the unknown probe, he both deflates the probe's mystery and his own aloof reclusiveness, making him more like a normal crew-member. Keeping the probe a mystery, even after its destruction, re-inforces that not only are there a set of named mysterious races in the B5 universe, but "unknown unknowns". We don't know what's out there!
Bringing in the vorlon cavalery also makes for bad story-telling. Anything can be fixed by a super-powerful being. I can recall only one instance of the Vorlons appearing as a "deus ex machina" in the series, and that was only to cut off a single-episode storyline.
Thirdspace fighter, powerful enemies of the vorlons and looks biological
Ranger vessel one million years into the future. Biological vorlon-like style to indicate that humans have reached the same level of development as the vorlons.
Markab transporter, cool but clearly metallic
The B5 designers drew on several tropes and trends to establish the ship design criteria. Bio-like textures and shapes were a big thing in 90's computer graphics. Biotechnology was also the next big thing in scifi, so making the elders masters of this made sense. But B5 (as well as Star Trek TNG) also makes use of the energy being trope. Namely that energy beings are the next level of development after biological sentience. If a species upgrade itself from wet meat to energy beings, such as the vorlons have done, there's an appealing symmetry in seeing their machines upgraded from base matter to living beings. The whole idea of ascending to energy has some deep roots in fiction which got covered in my answer to "
In Starcraft, are the Protoss inspired by anything special? "