From your descriptions it sounds like you are looking for Tycho's support for a manifest-first driven approach. I think such an approach is not possible yet, i.e. you have to have dependencies declared in targets in BUILD files.
Thus, the only support Bazel can provide is generating OSGi headers (with some genrule).
It might be doable to implement '.target' file based dependency fetching similar to maven_install but that's a lot of work. I found it easier to just remain within the ecosystem and use Tycho (even for the Bazel Eclipse plug-in).