I can't remember if Herptivite has D3, I don't think it does though. It should state on the bottle.
You are using calcium with D3? How often do you use that for your dragon & how old is your dragon under 3 months?
I don't use HerpaVite, I've got ReptiVite which is probably very similar. Wont hurt to mix with some calcium powder 2 - 3 days a week.
My beardies (all my lizards skinks and beardies infact) get mixed calcium + reptivite (1:1) about finger nail of each on a laboratory spatula (about 1/4 tsp I guess) 2 - 3 days per week as my insect dusting mix , other days it's just calcium and I give them a day off having their crickets dusted per week.
The insects come out of the dusting tub with a light dusting on them, the surplus dust in the tub after 2 or 3 days of insect dustings goes in with the mealworms and superworms on their bedding/food. No wastage.