Could you back this up with a link or something? I heavily followed the production of both of these Nolan Batman movies, and this was
Ice Cube (Friday After Next): Never, Evah, Evah, Evah
Mentioned in any of the conversations about the Batmobile's design being directly resembling a bat of ANY kind. I can take away alittle inspiration of the bat-cowl, but that extensive and over analyzation of that bat design was thought up by some fan a year after the design was brought to the public attention, and it was clear that said fan was trying to justify the car design having to resemble a bat in some form because traditionally most batmobiles represent an actual bat. This was never the case with the Tumbler. I remember hearing very specifically Nolan mentioning he was going for Humvee and a Lambo, a tank with elements of stealth bomber. Now you could say the design of the stealth bomber, which has a very bat like shape is about the only true bat design that would've influenced the Tumbler.
Now I might be wrong, but I highly doubt it. Not in the "Art of Batman Begins", the DVD section about the Tumbler was it mentioned that the design was made to look like a Bat with his wings folded. Ever. But like I said there is a slim chance I might be wrong, so if you could find proof to back your statement I'd be interested in seein and reading about it.