Using cobbler to provision Ubuntu systems is no problem when using Preseed, but it is a problem when using Kickstart Profiles (Ubuntu has had Kickstart compatibility since at least 10.04).
If you have ever created a Ubuntu cobbler distro tied to a cobbler profile pointing to a Kickstart Profile then tried to PXE boot a system from that cobbler profile, you have probably encountered the following error:
This occurs because in the tftp PXE boot entry (found in /var/lib/tftp/pxelinux.cfg/default) the append line pointing to the Kickstart Profile is written using url= and not ks=. Using url= causes the Ubuntu installer to expect a Preseed file, not a Kickstart Profile. If you have any CentOS profiles, you will notice their tftp PXE boot entry's append line is written using ks= and not url=.
When a cobbler profile is tagged as a Ubuntu distribution, cobbler will always output url=. You could manually change it to ks=, but running
cobbler sync at any point would overwrite your changes. There is probably a way to trick cobbler into thinking a Ubuntu profile is a CentOS profile, but that's more trouble than it's worth.
For some time, I had difficulty searching Google for a solution to this - if there even was one - or finding any discussion on it. As of September 2014, some discussion had finally appeared and the original poster has created a GitHub Issue to support selection of Preseed or Kickstart Profiles for distributions that support it. Assuming this feature is added in cobbler 3.0.0, an option will be available to specify Ubuntu profiles to use either Preseed or Kickstart Profiles.