Resolved this when I noticed that the ELB health checks were able to access the admin UI. The issue was that port 8983 was indeed blocked from the SSH machine, as that machine was located over a VPN tunnel into AWS. Our deployed applications had no issue accessing the test collection as they resided purely in AWS.
-- Sent from: http://lucene.472066.n3.nabble.com/Solr-User-f472068.html