i honestly dont think there are any nutrients in eco earth to begin with, i take it (based on assumption), that keepers say chams eat dirt for an intake of nutrients they arent getting else where, but in the wild i guess earth dirt has some sort of nutrition to it. even captive bred or captive hatched reptiles have wild caught instincts. but it isnt even a known fact that they eat dirt to intake more nutrients. many will advise you regardless to cover the dirt in your plants with river rocks, and avoid other substrates all together to avoid impactions of any sort.
boggles my mind at times though since you must keep a laying bin of sand and substrate for females... i dont know, might as well just do what the experienced keepers say. no use trying to debate.