There's a certain amount of "fair use" allowed from any site, unless they make it clear that you are not allowed to use any information in any way. Even then, fair use typically applies. However, it is generally not a good thing to copy word-for-word from anywhere, but better to summarize and then cite the original source. So my recommendation would be that unless you can find where Find-A-Grave got their original information (they don't have original sources at their site, so they got it from somewhere else), I wouldn't plagiarize their info, but reword, summarize, and cite.
