By safe you mean will they still have the music on them after they go through the machine? I would think so, the type of radiation and dose don't seem likely to cause loss in either memory chips or mini hard drives. I haven't lost anything with either my chip based mp3 player or my sd card camera. But you may want to check other sources to be sure.
I don't like taking small electronics out and putting them in the tray since they are easily stolen, besides they tell you to put them in your carryon bag. I don't like having to take my laptop out of the bag in the security line. There was a time when crooks would deliberately delay you at the metal detector so another crook could make off with your laptop.