It's impossible to say for me. Maybe a chemist would be of more help.
Like I said, they are selling it as an aqua scape product and state it's been tried and tested. It's hard for me to believe that they would put a product like this out there if it was going to leach chemicals. Seems like they would have a lot of very unhappy reefers at their doors in short order.
Personally, if I was worried about it leaching, I don't think I would trust drylock to stop that process.
I would call them, see if it's really been used for an extended period of time. Maybe get some references...