It is a bit hard to tell with the picture, but your substrate appears to be too dry, and you are correct that the likely cause is dehydration.
At the egg stage, these guys are not picky (at all) about what substrate they are in, *as long as they are moist*. Even sufficiently moist kitchen towel would do the trick as long as you swap out the paper towels to cleaner ones if the tissue starts to get moldy*. As for how moist - it should be about the same moisture content as how the soil would be if you first saturate it with water, then subsequently squeeze the substrate as hard as you can to drip out all sqeeze-able water. The resulting substrate from this process (after un-clumping them) is at a great moisture level for almost all dynastidae and lucanidae species.
It is possible to have larvae hatch on the surface of the soil, but for the exact reason you mentioned in the update (hydration) it's easier to keep them consistently moist deeper in the substrate. If you want to monitor their progress while keeping them deeper in the substrate, try making a few 1/3 inch dia x 1 inch deep** holes (with a pencil or a similarly shaped stick) in the substrate on the side of a clear container and put one egg in each of these holes. Although most non-isogenic D. granti are notorious for having huge variations in how long they take to hatch (a few weeks ~ 6 months) even from one laying female, this should give you a better idea of what the general batch-wide progress is like as long as you have more than just a couple to monitor.
Also, since I notice a fair bit of perlite, I'm going to hazard a guess that this substrate you are using might be used plant potting mix. Those perlite pebbles have a good chance of getting stuck in the digestive tracks of the larvae once they get large enough to ingest a small piece, since they are essentially glass crystals with microbubbles inside. In addition, plant potting mix tends to also have high nitrate concentration (and/or other components of NPK) depending on the degree to which they were used, so try using another substrate overall (fishkeepers can attest to the fact that what is a good concentration of chemicals for plants/algae is usually not good for animals). The eggs still appear have a fair bit to go until they hatch, so I think there will be enough time for you to go look for deciduous wood-based substrates, or get some from other breeders if you don't have them on hand.
As long as you moistened them enough, I think there's a good chance that most of the eggs will recover (maybe except some of them, like the super-dehydrated egg I see at the center of the picture).
Best of luck!
* You might be wondering at the back of your mind if the chemicals in the paper towel might do something. They may a bit, but for the purposes of rearing the beetles at the egg stage (and even a few days into the larval stage), it is fine (as for how I learned this - desperate times call for desperate measures -_-). There have been some studies (
http://11e.devbio.com/wt2104.html) where chemicals in paper linings caused insects to have extra larval stages in some true bugs (leading to the discovery of insect juvenile hormone analogs), but that is only when they were continuously exposed to the source throughout the entire larval period, which for our case will definitely not be true unless someone wants to try giving their D. granti larvae a totally different diet.
** About 8mm diameter x 2.5cm depth, for all you fans of SI units.
