Welcome @boinsoft, and thanks for your first post 
I cannot add much regarding bazel.
The only thing which comes to mind is that Eclipse Tycho - also an external build tool (based on Maven) - has added support for building bnd workspaces recently.
see
- tycho/tycho-bnd-plugin at main 路 eclipse-tycho/tycho 路 GitHub
- tycho/tycho-bnd-plugin/src/main/java/org/eclipse/tycho/bnd/mojos/BndBuildMojo.java at main 路 eclipse-tycho/tycho 路 GitHub
- Building bnd workspaces with pomless Maven via Eclipse Tycho
Tycho uses bndlib under the hood which is called by maven classes.
Maybe it can serve partly as a blue-print how another build tool does it, to adapt it to bazel.
And of course there are the existing maven plugins and gradle plugins from bnd itself.