I'm not sure of it myself, but I've read some forums say the glue is toxic in it's liquid state, but safe when it hardens and I've also read other forums talking about using hot glue guns to glue together coral in their saltwater tanks with success..... I suppose just make sure the glue sticks are non-toxic and if you get super ambitious with it, check out http://en.wikipedia.org/wiki/Hot-melt_adhesive
and see what the glue sticks are made out of. Once you do that, check to see if the ingredients are toxic and/or can leak into water and become toxic.... It's a bit of work, but imo well worth the effort and great knowledge to add to your own research.