Neo4j has a REST API and there are elixir wrappers like
https://github.com/florinpatrascu/neo4j_sips
if you do not want to use it directly. Gremlin runs on JVM so unless someone
decides to port it (there are people experimenting with similar ideas GitHub - jschoch/trabant: experimental gremlin pacer like graph traversals · GitHub obviously not ready for production use). GraphDB that will not be a fun stack to support. Another thing to consider is there a need for Graph database in the first place while in theory they should perform better then RDBMSes in reality depending on dataset and types of queries it’s often not the case.

there is also: GitHub - florinpatrascu/bolt_sips: Neo4j driver for Elixir · GitHub; a newer version of Neo4j.Sips, focusing on using the Bolt protocol. Where Bolt is: Neo4j’s newest network protocol, designed for performance. HTH

I have only used OrientDB with Python but there are two libraries for it in Elixir: marco_polo and ex_orient. I hope that helps.