The Mac binaries for the SkookumScript API and plugin are available via the Unreal Marketplace and from our GitHub repository.
We have not been actively testing the Mac binaries with each release though they should work.
Currently you need to compile the SkookumScript script binaries using the Windows SkookumIDE. You could also use the Windows SkookumIDE to connect to the Mac UE4 runtime when it is using the SkookumScript plugin. You need to run the SkookumIDE on Windows or Wine (not tested for some time).
You can have the SkookumIDE copy the compiled script binaries to a drive shared with your Mac. You can even dual-boot if that is the only option.
[Output] section of your project .ini file you can specify one or more directories for the SkookumIDE to copy the binaries:
In the future, either we will get the SkookumIDE running natively on the Mac (and Linux) soon after the new Slate version of the SkookumIDE is available for Windows or we will release a command line version of a simpler SkookumScript compiler that will work for Mac (and Linux) to bridge the gap.
So SkookumScript development on a Mac is possible though currently a pain.