HI Russell,
The first answer is yes, if you need sudo you need to add it as a dependency. The builds on the farm will only build with your declared dependencies. The prerelease has a minimal bootstrap which gives you command line capabilities for debugging presumably includes sudo for that purpose.) You will probably also want to add a build-depend rosdep rule for libcap2-bin to make sure the setcap is installed.
While looking at this, do you know if setcap is portable across machines, aka if executed on the build machine will the attributes persist through the debian install process?
Tully