Are there any universal lessons to be taught in Guns, Germs, and Steel?
I think this depends on how much one is willing to take Diamond's opinions as universal lessons. Diamond presents a few things that he considers to be, if not universal truths, then at least very consistent patterns among human behavior and civilization, as well as several precepts that are universally accepted among his peers.
For example, Diamond and his peers generally accept that all humans are "equal" in the sense that all groups possess equal intelligence and intellectual ability. This is strongly asserted because it is central to Diamond's argument that the dominance of Western civilization has nothing to do with the "white" race. However I think this entire line of research is suspect, because what researcher in the modern age could possibly do this kind of research, let alone come up with dissenting results, without being ostracized as a racist? The well is poisoned, so to speak, and it should be recognized that the "universal truth" of human genetic and physiological equality has at least as much to do with our social standards as it does with empirical research.
The universal truth that Diamond tries very, very hard to articulate is that geography is the final determiner of the success and dominance of various cultures and civilizations. However this is also one of the most frequently contested of his points, and I would consider it far from a universal truth because the degrees to which Diamond must go to link geography to genocide defies reasonable connectivity.
So ultimately, I think there are few if any universal truths in this book that are not actively contested by the academic community.