I have not found anything to use for tags in FTM besides custom facts. I'm not sure if I would be in favor of tags in FTM - depending on how they would interface with Gedcom and transferring data to and from other programs.
For example, I have many ancestral lines in my file (my personal ancestral lines approach 200 - mostly New England immigrants in the 1600s.) If I want to list all Civil War vets who were casualties that I share Hallock blood with who fought on the Union side, I have a custom fact I call Military Filter. I could call it Military Tag.
Military Filter: Civil War Union Hallock Casualty
or I have a person I share 3 ancestral lines with:
Military Filter: Civil War Confederate Smith Taylor Jones Survived
I can filter for any or a mixture of these text strings in the regular FTM filter used at the bottom of the Index, or in Custom and other reports, or in exports.
For example, when I do a filter in the Family Tab of the People Workspace for "other filter", Military Filter, and search contains all terms Hallock Civil War, I find:
I have 67 persons from my Hallock line in the Civil War
Filter for Civil War, Hallock, Casualty:
17 died during the war
Filter for Civil War Hallock Confed, I find:
3 served in the Confederacy
BTW, I track spouses of family members as members of the family for this purpose.