This very much depends on what you mean by the first "oracle webcenter" and what kind of integration you are looking for.
Oracle WebCenter contains three main product lines:
- Oracle WebCenter Portal,
- Oracle WebCenter Sites,
- and Oracle WebCenter Content.
Since the newest version 126.96.36.199 it is possible to store Sites' assets in WebCenter Content.
WebCenter Portal, where the name WebCenter originated from, is another front-end technology, so it would rather co-exist next to Sites than integrate with them. See this thread WebCenter Portal and WebCenter Sites Integration for more details.