Update, January 21, 2013: YES, it was! Scroll down for links to the entire saga.
Because it’s doing a hell of an impression of one, if not. It’s got the huge cervical rib loops (wings), bifurcated neural spine (top fins), and even a condyle on the front of the centrum (cockpit pod). About all it’s missing are the zygapophyses and the cervical ribs themselves.
Some actual Apatosaurus cervicals for comparison, from previous posts:

Apatosaurus ajax NSMT-PV 20375, cervical vertebrae 3, 6 and 7 in anterior and posterior views. Modified from Upchurch et al. (2005: plate 2)

Apatosaurus parvus CM 563/UWGM 15556 cervicals 7, 5, 4 and 3 in anterior and right lateral views, from Gilmore (1936:pl. 31)
And of course Mike’s magisterial work photographing the Apatosaurus ajax holotype YPM 1860 cervical:
More on the Umbaran Starfighter here.
The complete Umbaran Starfighter Saga–at least as told on SV-POW!:
- Was the Umbaran Starfighter from Clone Wars inspired by an Apatosaurus vertebra? (Dec. 13, 2012)
- Heck, yes, the Umbaran Starfighter from Clone Wars was inspired by an Apatosaurus vertebra (Dec. 15, 2012)
- Umbaran Starfighter vs. Apatosaurus cervical, round 3 (Dec. 16, 2012)
- Umbaran Starfighter update (Jan. 4, 2013)
- CONFIRMED: the Umbaran Starfighter is an Apatosaurus cervical (Jan. 21, 2013)
For other Star Wars/paleontology crossovers, please see:
The sauropods of Star Wars: Special Edition
and–mostly as shameless self-promotion since the paleo link is pretty tenuous:
References
- Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175-300.
- Upchurch, P., Tomida, Y., and Barrett, P.M. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No. 26. Tokyo. ISSN 1342-9574.
- Wedel, M.J., and Sanders, R.K. 2002. Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus. PaleoBios 22(3):1-6.