Hi Cheri,
Im not familiar with edible glitter, but if its like sprinkles or decorations for candy and cookies, yes, you can use it in resin. I would recommend sealing them first (the resin gloss spray works great for this, but we cant ship that product overseas). You can try a glue paint on sealant for this process.
I know that sounds like overkill, but whenever Ive used edible products in resin, the castings looked great for months, then started to leach out and/or change color almost a year after they were cast.
If there are others doing this technique, I would love to hear what your experience has been.