Hi Marc,
Everyone will need the integration code in their engine build, but only the sound designer(s) will need the Wwise project. The beauty of Wwise's UE4 integration is that UE4 builds the banks into UE4 assets using the wwise sdk files. The Wwise project folder is needed to build the banks within the UE4 editor, however once they're built, they will be useable for anyone who has UE4 with Wwise integration.
So everyone else on the team WILL still need the same UE4+Wwise build. As far as the UE4 licensing goes for useage, I am assuming you can still version control your entire UE4 source for your whole team, if they have subscriptions. Perhaps someone else could clarify this. If not, each team member would need to add the Wwise integration files to their own UE4 build.