Greywolf1: Yes, the answer is clear enough. Am I right to assume that all other add-on quests not contained but playable in classic Daggerfall can't be played in DFU - unless they are contained in a DFU mod (like the DF Quest Pack mods)?
On UESP, it says that mods for classic Daggerfall have limited functionality. So it depends on the individual mod how well it will run. ([url=https://en.uesp.net/wiki/Daggerfall_Mod:Daggerfall_Unity/Installing_Mods]https://en.uesp.net/wiki/Daggerfall_Mod:Daggerfall_Unity/Installing_Mods[/url])
Thankfully, as others mentioned, there is already a Daggerfall Unity mod for the other add-on quests (the ones included in DaggerfallSetup). Since the modders who set up the DFU version were unable to get in contact with the original quest modders, the DFU version can't be uploaded to Nexus Mods, but it can be found here:
https://forums.dfworkshop.net/viewtopic.php?t=3643