First off: Live moss in a Leo enclosure... what? Moss requires high moisture, low temps, and high light intensity to grow well. Your leo on the other hand, needs very low humidity, high temps, and not too much light really. So live moss is pretty pointless and impossible to keep in a leo vivarium. It does quite well in poison dart frog or small gecko species terariums however.
As for the white bug, it was most likely a springtail as was previously said, in which case it is fine... but it doesn't really matter what it was, cause the moss won't stay in your leo enclosure anyway right?