According to [this page](https://neo4j.com/editions/) it's not. In fact, they are restricting important functionalities to their Enterprise Edition exclusively. Which means, the codebase is not the same.
You can see it here: http://github.com/neo4j/neo4j
See how there are 'community' and 'enterprise' top-level directories? The 'enterprise' directory contains the enterprise-specific code. It's a separate project in some senses but it does share the same repository, and it is open source.
As you can also see by looking at that repository, the Enterprise Edition is licensed as AGPL. Here is the license: https://github.com/neo4j/neo4j/blob/3.3/enterprise/LICENSE.t...
I'll quote:
If you have not executed a Commercial Agreement with Neo Technology, the
Software is subject to the terms of the GNU AFFERO
GENERAL PUBLIC LICENSE
Version 3, as follows: