My question is, I am not able to copy jars from 3.x's hotdeploy to 4.x's deploy, the deployment isnt successful.
Is it right to conclude that I need to change all my deployables to OSGi bundles to have the same ones working in 4.x?
No, you needn't use osgi bundle package for your JBI SA.
All JBI packaged SA should work by default.
What's the error you encounter?