There is an ongoing project to enable OBS to check out code from CVS, SVN, etc. It was worked on during the
Hackweek. But it does not completely automate the system because 1) there is no way to schedule it to run when the upstream code is updated atm and 2) it can't figure out the version of the code it has just checked out and so cannot update the specfiles for you.
But you could probably knock up a script to work with a specific project using this as a base ...