I’ve just built a quick Rails app to try to duplicate your problem, but everything worked fine for me (here’s my minimal model). I was using Paperclip 3.4.2 with the default filesystem storage backend and Delayed::Job 3.0.5.
What Paperclip storage backend are you using?
Also, have you tried running an isolated test that only sets an image_remote_url and does nothing else? Something like this:
rails runner 'Deal.delay.create! image_remote_url: "http://georgebrock.com/images/thumbsup.gif"'
rake jobs:workoff