Mr Dylan has done a lot of recycling over the years. As well as some of the examples quoted above his "I pity the poor emigrant" is sung to the air of Tramps and Hawkers, and there are quite a few others.

One of the songs on his latest album is to the air of "Red Sails in the Sunset", by Irish songwriter Jimmy Kennedy. I don't think he has ever sought to disguise the fact that a lot of his material is borrowed from the tradition, but attribution has not always been as accurate as it might.

As for Metallica and Thin Lizzy, it is more or less a direct lift from the Thin Lizzy version of the song. I used to own a copy of the Thin Lizzy single, but I have no idea whether they attributed it to Mr. Trad or not. It is a pretty distinctive arrangement.