At a high level-
Import-Package is for importing available dependencies when the state of osgi bundle is changed during its lifecycle in the container (Felix), Version 0.0.0 indicates that it should start from the lowest version, pick whatever version is available as mentioned in manifest and satisfy the dependency at runtime in Felix.
The packages mentioned here may/may not be available/packaged within the bundle but may be available/registered in Felix
You may choose to control it at a granular level that import * but not one package or something similar to that. import-package is required to create the manifest file properties
Dependency on other hand works with dependency management to download the packages in local repo/nexus etc. and to mark that a particular bundle should be applied at specific scope mentioned inside <scope>. It defines the scopes of dependent bundles and which can again be superseded with import-package configuration to allow/deny the packaging of that bundle