Not yet but it is on our list of things to do. https://github.com/designcreateplay/NodeBB/issues/563cnvo created this issue in designcreateplay/NodeBB closed Saving uploaded images to disk vs Imgur #563
Upload Images to S3
I would love to be able to accept images on my forum, if they were to be uploaded to an S3 bucket.
I will probably look into this for 0.3.1. Also see https://github.com/designcreateplay/NodeBB/issues/563