Connecting UF wiring for under deck lighting to an existing NM exterior light switch
Yes, in fact, UF wire can be treated just like NM wire when ran indoors.
340.10 Uses Permitted
4. Installed as nonmetallic-sheathed cable. Where so installed, the installation and conductor requirements shall comply with Parts II and III of Article 334 and shall be of the multiconductor type.
Including the ampacity adjustment in 334.80.