Got a reply from the manufactuer.
"Good Morning Brian,
Many consumers have successfully applied Plasti Dip to different items in their aquariums. Plasti Dip is considered non-toxic once fully cured and dry; 24 hours after final coat is applied. Plasti Dip can be used on many different substrates such as wood, metal, stainless steel, plastics, fiberglass, glass, and much more. We recommend testing this application in a small area to make sure it will meet your expectations.
Thank you,
Tiffany Werner
Customer Service/Technical Support/Inside Sales | Plasti Dip International"
That is a pretty bold affirmative from the company. I think that they wouldn't say that if it wasn't 100% safe.