If they're free, I say why not try. But, black eyed susans don't like to be moved. I planted 9 of them this year, 4 died, 3 were borderline for about 2 months (some went down to 1 leaf, but there's new growth now I think they'll make it). I purchased another 2 to make up for the lost ones but this time knowing how difficult they are and how much they hate to be moved really worked up the hole with a lot of compost & organic fertilizer and they seem to have taken well. My co-worker seperated them, and all her transfers died.
So, make sure you put them in really good dirt with compost and sprinkle organic fertilizer in the mix as well, and you'll need to water them almost daily for a couple weeks but don't be surprised to have heavy losses. Maybe others have had more luck with them.
If they are the big Indian Summers they are touchy. I have those and the old tried and true standard blackeyed susans. I started the standards down by my creek where they multiplied like crazy. I've since moved clumps to several other locations and had wonderful results. As stated, this late in the summer just keep them well watered. I think they put on a magnificant show when they get size to them and they are so easy.