Do these work on Dwilight?
During the third invasion when the portal stones were active, they were a manual process. My understanding is that when you activated them, there was no immediate effect. A message was sent to Tom/GMs, and they would have to log in and manually do whatever it is that they were supposed to do, based on where they were activated. If there was no portal in the region, then you got some message about there being no effect, or something about the magic "pointing to the east", and supposedly pointing to the nearest portal.
If someone were to use portal stones now on Dwilight, I would imagine that nothing would happen at all. Remember that the Dwilight daimons are supposedly a completely different race than the BT daimons. So there's no reason to assume that doing the same thing on the two islands would necessarily produce the same results.
But, you really never know. Maybe the Dwilight daimons are lying.