Tears For Mor Dhona by Nobuo Uematsu is actually, as the name suggests, the old Mor Dhona zone BGM theme from the original version of FFXIV (version 1.0). In fact, much of the Palace of the Dead music is actually old version 1.0 tracks, including quite a few that have not actually been used anywhere else in ARR.

And speaking of 1.0 Mor Dhona music, the other track you asked for in your first post might be Phantoms on the Lake, also by Nobuo Uematsu, which was the 1.0 Mor Dhona battle theme. A greatly abridged version appears elsewhere in ARR in certain dungeons, such as Diabolos's battle theme at the end of Lost City of Amdapor (NM), retitled as 'Persistence' on the Before the Fall OST, but this version is missing the slower, lighter second half of the track that you mentioned.