Requiring specific experience with co-habbing these two species is like requiring specific experience for telling someone not to take a shower with their iphone 6 without a waterproof case. Documentation is limited to non-existent because it's well enough covered by the general rule of don't put your electronics in water that people don't try it just because sometimes it maybe survives. It's an Australian skink and a New Calcedonian gecko. They would not overlap in the wild at any point. They can carry bacterial loads that the other would not have been exposed to. In general, animals can safely and normally carry certain bacteria that other species would be highly susceptible to. What gut bacteria or skin bacteria do these two species carry? Who knows. It's certainly not studied for the skink and probably not for the gecko.
The skink isn't even herbivorous. Even many herbivores are less strict than people think - even deer have been documented eating meat. Pink tongue skinks are said to be fully willing to eat beef, dog food, cat food, and chicken in captivity. They are clearly not that picky about their diet.
Here's another species of skink eating a gecko if that's more compelling for you. I wasn't able to actually watch this at this time, but am putting it out there anyway.
https://www.youtube.com/watch?v=4wdgQAwUdfY
Animals explore things with their mouths. A curious skink could kill a crested gecko without trying to eat it at all, just checking it out.
People will generally not propose ideas on how to improve this plan that are not "keep them separated" as it is unethical to facilitate an unethical plan. There are extremely few individuals out there with the expertise to create community tanks properly and every single one of those tanks begins with species that share a range naturally. No research will turn up knowledge that simply doesn't exist, there is no way to gain the expertise to cohab these animals. It MAY be possible to gain the expertise to cohab different species with the same native range, but it would take years and funds.
