Probably not. There is a fundamental difference between a NAS and a DAS
. (and an USB disk is a DAS).
A NAS serves files. The client computer does not need to know which filesystem the server uses internally (fortunately. The filesystems used be 99% of the NASses are not supported by Windows PC's).
A DAS only serves a large number of sectors. It's up to the client to organize that in a filesystem. And, important, the client of a DAS is the only one
accessing these sectors.
For this reason a NAS cannot share the same data both over network and USB. If the USB client would change anything, the NAS wouldn't know that, and vice versa. The filesystem would soon crash.
The closest solution I know of is the Lacie Network Space 2. This NAS can offer a part of it's storage via USB. But as soon as you connect the USB cable, you cannot access the data via network. You'll have to pull the cable to get network access again.
Well, if you always have to pull the cable, you could as well use an external disk connected to your NAS.