In some way, the libusb is precisely meant to hide these
  differences. Wherefore, a new question : is it possible to design a
  special libusb which, even though being a Linux type library, would
  translate into native NetBSD kernel USB calls.

You could probably compile libusb under linux (with a cross compiler,
perhaps using the real linux cc in the chroot, but with netbsd usb .h
files), and bash configure output to use the netbsd kernel usb
methods.

But, this will only make linux programs that use dynamically linked
libusb.  This would almost certainly leave out things like vmware.
To me, the point of linux emulation is things I can't compile
natively, and it seems the special libusb won't help much of that.

-- 
        Greg Troxel <gdt@ir.bbn.com>