However, IIUC, Bazel doesn’t support dynamic deps, so it seems quite inconvenient (if that’s true) to have to handle ocamldep not as part of the build rules but as part of the rules generation themselves.
Yep. Most of the existing Bazel rules packages thrown up on Github will just recompile all the .ml and .mli files in a target if one of them or their transitive dependency tree is touched. Really suboptimal.