Are you using the objective C package from the official Slack 11 repository? It should work with the gcc-g++ tools in VL, since those are borrowed from Papa Slack.
HTH a bit,
That's what I'm doing for now. I had no idea that the gcc toolchain packages came directly from Slackware, but it seems to be working. There are only a runtime library, binary dispatched from gcc (cc1obj) and a few header files. (Strange how STL comes with C++ by default, but not OpenStep standard libraries for Obj C...