I have three OpenCL SDK installed side by side on one machine (Intel CPU + Nvdia + AMD). Works flawlessly as long as you pay attention to issues such as which CL.h header you use and which libOpenCL you link to (these should be indistinguishable in theory, but aren’t in practice). You can even easily switch runtimes by parametrizing your build system with a set of environment variables specifying the directories for these.