Surely the Hallowe'en, All Souls tradition is about remembering or being revisited by the dead: whether they are beloved ghosts or ancestors. So any song with ghosts or revenants-- Sweet William's Ghost,
the Wife of Usher's Well,
any number of night-visiting songs,
The Unquiet Grave,
She Moved Through the Fair,
Lowlands Away,
Molly Malone,
even stretching it, Joe Hill.

Or how about Poor Roger/Oliver Cromwell buried and dead with an apple tree over his head?

As others have pointed out Halloween is linked with Martinmas and Remembrance Day traditions too,

Violet Jacob's wonderful Halowe'en poem as sung by Karine Polwart or Jean Redpath links the two traditions. But seems to me a lot of those laments for the war dead fit in with that late autumn tradition.

Will Ye Go to Flanders?,
The Bonnie Light-Horseman,
Shule Agra.

Of course, there is a ghoulie, long-leggedy beastie tradition too, and witches if you want. I did once sing Woman by the Churchyard Wall at a Folk Club. It wasn't well received, though everybody I spoke to agreed it was one they had learned in the oral tradition in the school playground, it somehow did not quite count as 'Folk'.