It's still a bit of a minefield. Don't assume, because a traditional song may be PD in some forms, that it is always so; many versions may have been first published relatively recently and be, in those forms, in copyright. In practice nobody who actually does have a direct interest is likely to chase you, but it is no bad thing to do the research so that you know where you are. Organisations like the Harry Fox agency and the Performing Rights Society tend to assume that, if a song has the same title as something they have on their books, that it must be the same song, and that you owe them money. On the other hand, it's also true that quite a lot of songs widely thought to be old and traditional are nothing of the kind; sometimes Fox and PRS are in the right.