As long they are focused to infinity there is no risk but when focusing to a pinpoint you will get the housing melted.Correct me if I am wrong, but you may not want to use an acrylic lens with a 1W 638nm, at least not for very long.
So for static focused builds there you can also use acrylic as well but I also prefer glas lenses because they can be cleaned easier and do not get scratched that easy.