Does Cypher's ORDER BY uses the index?

As of now, neo4j does not take advantage of an existing index to speed up the ORDER BY clause.

You should probably let the neo4j folks know you would like this to be supported :-).

[UPDATE]

There is, as of this update (Jan. 10, 2018), an open feature request for this capability. According to a recent comment, it is supposed to be a "high prioritized feature".