I am making a cake that will have chocolate carpenter tools, nuts and bolts on it. I read that I should use highlighter dust to give them the silvery sheen look. I have everything dusted, and now I am reading that it is non-edible. I was going to place the tools on the cake, will this be safe? Obviously, we won't be eating the tools, but will the cake be ok, or do I need to start over and use luster dust instead? Grrrrr...

I found this link about the dust that says it's non-toxic and considered edible in Europe but not in the US. It says that it is at your own discretion if you eat it. I think it would most likely be ok to still put the decor on the cake but eating them is up to you.
http://www.sugarcraft.com/catalog/coloring/dusts.htm#highlighter

Can you put something between the cake and the tools? Maybe cover a piece of cardboard with fondant or even buttercream.

Its not FDA approved, but that doesnt mean its not edible. I think the small amount you use doesnt matter,I guess if someone took the entire little jar and ate it, it might make them feel a little queezie...