I don't know what people are talking about in terms of any risk, but its complete rubbish. Theres no risk whatsoever of connecting the line out of a radio to the line in of a soundcard.
Think about it. If there was any risk then nobody could possibly make any music, as plugging the output of a synth into your soundcard might kill you.
If there was any possible danger to you in touching something thats connected to a mains powered soundcard, mixer or amp, then nobody could play the electric guitar!
The only time there could possibly be any danger would be if something had gone so catastrophically wrong with your soundcard that it would either have blown its fuse, or just blown up.
You don't need any kind of transformer. Just plug the radio output into the soundcard and adjust the input level to suit, or turn down the radio if the level is too high.