This is a problem we never had to deal with until storyboards were introduced - Whenever there was a chance of conflict in UI, we just made sure that no 2 developers ever wo
Is this about merging XML files?
Fortunately, SVN allows you to change the merge tool you use to perform merging for different types of file. (eg tutorial for using P4Merge)
So now you just need to find a great tool for merging XML files (good luck :) )
there's WinMerge (with the DisplayXMLFiles prefilter), or diffxml, or XMLMerger or a java xmlmerge tool