Yes and no. The MacRelix toolchain does, in a very trivial sense, generate Metrowerks-compatible object files, because mwcc is ultimately a wrapper around the Metrowerks-proprietary MWC68K and MWCPPC tools that run in MPW.

I reverse-engineered enough of the .o header format so that MacRelix's ar and ld could retrieve architecture and runtime information from a static library instead of making the caller provide it via a switch.

Separately, I've been writing post-linkers that patch or rewrite the Metrowerks-provided startup code in 68K code resources. The next step on this path might be writing my own compatible linker.