Glitter Glue?

I cannot speak for this particular brand, but as a general warning: a lot of glues do not age well, especially when exposed to light and air. That means they might yellow, get brittle or become sticky to the touch. The latter is something it might even have right from the start. I often felt like especially cheaper craft glues suffer from that, since they're not exactly meant to be long lasting.

I would definitely seal before and after using the glue, just to ensure that the resin has the best chance not to get harmed. The glue is probably mild enough not to eat away the sealant or stain it. Keep in mind though that drawing on ornaments like that can cause uneven, patterned yellowing too (if the glue is somewhat opaque due the glitter). If no light can pass through the glue, areas underneath will yellow slower than the exposed parts.