Are the DLC Scenarios playable as scenarios

[Johnus]

Can you play them as "scenarios" as opposed to in the campaign only?

[KerenskyLI]

Yup, the campaign maps are playable as single scenarios.  Use the same method as you would to play the 10 MP scenarios as solo play.  Find the map files from where you installed them, and move them to the "scenario" directory.

For me on Windows XP, it's
C:\Documents and Settings\Owner\My Documents\My Games\Panzer Corps\Scenario

However, like the 10 MP maps, these campaign maps were not expressly designed for solo play.  So while they do work, they are not optimal for this type of play.
Hence the manual step for activation. 

[Rosseau]

I imagine you can do some AI work in the editor to make them better.