This particular address is donation address for the Ghost Security Group, not IS.
I agree, I'm very sceptical about authenticity of this story. They rely on anonymous source and fail to provide the address(es) in question.
To me, it looks like made-up controversy to drive more traffic.
That being said, it's perfectly possible that someone organised BTC donation address for IS, but I don't think the IS would have much use of bitcoins, unless they were able to cross the borders with countries with BTC/fiat exchanges. Even if, I don't think they would bother, as they did have much larger revenue source.