To the best of my knowledge, and it is limited, once a body is creamated it is not considered to have any hazardous material. So it isn't illeagle but to some it can be creepy. I know a number of people that have had their ashes scattered in the oceans and Chris and Chrisy had theirs scattered at Ginnie if I'm not mistaken. Go for it, and make sure you watch for unexpected gust of winds. My father in law got the last laugh in on us as we scattered his ashes. An unexpected gust got him blown back all over us. We scattered the last of him down the washing machine that night.
LOL I have heard of that happening to other people too. I Have to say that would be a intersting occurence!