Well, they aren't likely to be active in the field of Climate Science and be seen on this petition unless they want their funding to disappear. Doesn't mean they can't have an opinion. However, the aim of the thing is to deny the consensus. To do away with the false argument 'the science is settled'. Even in the case of a physical law, the science is only settled until it is challenged, as Einstein challenged Newton. The correct stance of a true scientist of whatever specialty is scepticism.
There is plenty of evidence that on both sides of the AGW question are people who are so heavily invested in their position that their objectivity is in doubt. Climate scientists who will not release their data or methods, only the conclusions, or who run climate models which have never been subject to proper quality assurance are part of the problem. The debate isn't over, and in any field of activity (AGW or EU, for example) anybody who claims the debate is over is probably a liar and a cheat.
They can have an opinion - how relevant is it is is another matter.