Sure, if you have 1 storyboard for your entire app, and 9 people are working on it, you will have collisions. 9 people on an iOS project is bound to have merge conflicts in code too, unless it's coordinated.
Xcode 7's storyboard references should help avoid some conflicts here, as it breaks up a single, conflict-magnet file into several. Hell, you can organize them like XIB files before Apple started pushing the 1 storyboard "simple" approach to ease the learning curve.
Side note: The title of this post should have been "Reasons we are switching away from Interface Builder", as it doesn't actually answer the question. But then it wouldn't be interesting enough to click on.