To get ArcEm to run on Mac OS 9 would require a new port - there's no easy way to convert the Objective C and Cocoa port that I've done to run with the old Carbon libraries. So yes, it is possible to make such a port, but it would be a new project.
Of course, the core of ArcEm is written in nice clean gcc friendly C; it is that around which I wrote the Cocoa front end. So a Carbon port shouldn't be too difficult. However, I'm not going to be the person to do it, sorry