The Concrete and Clay Roof Tile Installation Manual for Moderate Climate Regions from RTI (Roof Tile Institute) gives two options for hip and ridge installations, on allows not using mortar, it states: (underlining is mine)
Openings at hips, ridges and head walls including chimneys, skylights, solar panels, and downslope horizontal abutments
shall be fitted with a weather blocking material to keep water on the surface of the field tile. Other methods approved by the local building official will be allowed. See Technical Bulletin at
rooftile.org.
If that material is not installed such that: 1) it is weather blocking; 2) keeps the water on the surface of the field tile; then check with the building official to see if, in his infinite wisdom, he has allowed less.