Нашёл интересный текст. Аффтар довольно уверенно утверждает, что использование произвольных VID/PID не является незаконным, но предупреждает о технических проблемах при совпадении VID/PID -> http://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2011/yl478_clt67/yl478_clt67/yl478_clt67_files/displaycontrol/usbdrv/USB-ID-FAQ.txt
Since it is so important that USB IDs are unique, the USB Implementers Forum,
Inc. (usb.org) needs a way to enforce this legally. It is not forbidden by
law to build a device and assign it any random numbers as IDs. Usb.org
therefore needs an agreement to regulate the use of USB IDs. The agreement
binds only parties who agreed to it, of course. Everybody else is free to use
any numbers for their IDs.