@JYost The images themselves have not much to do with the fog-client software. It just does the host management (reboot on imaging tasks, domain join and so on).
But I do understand your question! Between 1.5.0 and 1.5.8 there were many changes in FOG and FOS (FOG Linux OS) which does all the actual work when imaging. We moved to newer versions with many tools in FOS, especially also partclone. But as far as our testing shows you should be able to use your old images without any change. Give it a try, just do a deployment to one of your hosts and see if it works. It should.