The PaCifiST ST emulator for the PC can read the disks and run the tools. The object formats produced by these tools are the same as those produced by the CP/M-68K tools and as such it should be possible to use these tools to get a CP/M-68K system up and running. This is basically the ALCYON C compiler and tools for CP/M-68K recompiled to run under GEMDOS.
Here is the GEM Developers Kit for the Atari ST.