Crickets are a tricky bunch, regardless of developmental stage. "Dusting" while commonly quoted, generally refers to food for terrestrial reptiles in my experience.
It depends on the supplement dusting the cricket. I've used some supplements and had aquatic caudates such as Cynops cyanurus take the dusted cricket off the top of the water so depending on the animal there are probable benefits to the consuming animal.
I believe that the CC chart quoted above refers to the fact that many different people feed their crickets many different things and to many different things.While there is some debate even now on the topic of "gut loading",
There is more argument over what "gut loading" actually means than the actual practice. Gut loading is actually a techical term that in the peer reviewed literature means one thing and one thing only... a diet that is fed to an invertebrate in an attempt to modify the calcium to phosphorus ratio of the invertebrate. A comprehensive review of the literature both historical and current with specific reference to crickets indicates that this is possible but requires strict controls and causes a high mortality in the crickets (the crickets have to be offered the high calcium diet as the only food source (not even fruit as a water source) as they would prefer to eat anything else but the diet for a minimum of 48 hours at kept as close to 80 F as possible. The crickets have to then be fed out before 72 hours as the crickets start to die from the high calcium diet after that point.
In the hobby, gut loading means that you have fed the crickets some diet that you percieve to be nutritious to the consuming animal before feeding out the crickets. This does have some value as crickets on analysis have been shown to be lacking in nutrients and allowing the crickets to feed for 48 hours allows the crickets to replace the nutrients that were lost. As a consequece there are a multitude of gut loading diets.. few if any have had the crickets analyzed to demonstrate what nutritional value they are providing to the consuming animal....
As for crickets being nutritionally poor, I feel this is dependent on what they are being fed to, Axolotls would not normally consume crickets or other terrestrial insects in the wild. Their digestive tracts do not handle chitinous exoskeletons very well. They would have access to many types of worms and aquatic invertebrates.
There is new analysis out that indicates that the amount of chitin in all of the analyzed insects has been overestimated by a factor of as much as 5 times. In addition, I am surprised that people consider crickets to have more chitin than say a dragon fly larva, or diving beetle. I have a hard time believing that axolotls would have a significantly different digestive tract than other padeomorphic Ambystoma (see for one example the reference
http://www.jstor.org/pss/30054443 )
Oddly enough amphibian nutrition is something of an interest of mine and I have been refining what I know for awhile now...
Ed