as the arbitrator engages on behalf of one side of the dispute

No - the arbitrator may be empanelled because of one only side, the arbitrator has to take both sides. Taking a snippet of RDR:

The Arbitrator is required to:

1. Be independent;
2. Maintain the balance of power between the parties,
3. Give each party the appropriate opportunity to present their case and to respond to the presentations of other parties,
4. Conduct a fair and efficient process, and avoid unnecessary delay and expense,
5. Keep all communications in the case file.

These rules are typical of those found in all arbitrations around the world.