Hi Martinez,
I am not an expert in Fluentd but as much as it is able to ingest JSON data and output events to Elasticsearch the integration won't be hard, feel free to share your entire use case here so we can help.
Are you using Fluentd instead of Logstash but at the end sending events to Elasticsearch? I think it is always good to use software from the same vendor to increase compatibility (Logstash->Elasticsearch).
Maybe you can elaborate the infrastructure you have in mind.
Regards,
Pedro 'snaow' Sanchez.