Possibly, but not absolutely.
The Nano was announced at a special event in conjunction with the ROKR. The Nano already took the wind out of the ROKR's wings, I doubt Motorola would have wanted even more Apple hardware to debut then.
Also, it makes perfect sense to introduce the Nano by itself and give it prime media time, and then introduce a new iPod (and/or Mac updates.) Had the Nano come out at the same time as the iPod Video, either or both would have gotten short thrift in the press. Both are very newsworthy, and very important products for Apple (the Nano especially, since it replaced Apple's best-selling iPod.)
At the very same time the Nano was introduced, almost all iPod billboards were replaced with Nano billboards. They couldn't have done this with a combined rollout.
Finally, there have been rumors for at least a couple of weeks that the iPod Video would be introduced in early October.