Hi!
This seems to be related to:
Looking at the source of sonar-scm-git-plugin, I understand that actually it’s not strictly “adding exclusions based on project’s .gitignore”, but instead it’s ignoring every file that’s not managed by the root repository.
You can verify this running git ls-tree -r HEAD in your git repo. The submodule’s files are not listed and basically this is what the Git Plugin 1.8 is doing.