It's difficult to find a definitive answer, but maybe we'll be able to extrapolate from this post by a Microsoft MVP (emphasis mine):
(...) you don't have to change MS's VID/PID anymore if
you use USB RNDIS to use ActiveSync.
Here's the official response from
Microsoft on this subject (as asked by a fellow MVP regarding a client
who had the same issue):
Question: Should they use the Microsoft PIDVID or create their own? If
they create their own, it means modifying the current .inf file and
therefore this means the driver will be unsigned and therefore may not
be able to be installed. In the past the Microsoft PIDVID gave warnings
to not use this. Now in 6.0 the warnings do not appear.
Answer: The answer is exactly the same as for Windows Mobile: For
ActiveSync usage, YES, you can use Microsoft's VID & PID for your scenario.
This is a change from documentation which says to get your own PID &
VID. Contrary to what the sample Registry file says, the OEM should ship
the device using Microsoft's VID & PID for USB-Serial ActiveSync client.
The latest OEM documentation confirms this (...)
Now, since you don't specifically mention ActiveSync, my understanding is that the above probably does not apply to your use case, which again means you will have to use your own VID and PID.
If you already own a VID/PID combination, I don't see any (legal) issues using this with RNDIS as well. It is the same device after all, and the USB host would load one of two different class (not custom) drivers to communicate with the device.
However, if you use your own VID/PID you will have to either
- supply a signed INF file to end-users that contains your custom VID/PID, or
- instruct users to manually select the RNDIS driver when your device is connected to the PC for the first time