Yep, you can't of course rely on OpenCL support, you have to provide a fallback. But are there any issues with including the SDK supplied OpenCL ICDs with the APK, for use with validated GPUs?
You are not allowed to ship drivers like that, and since version 7, there is kernel validation about stable NDK APIs.
So yeah just because there is an OpenCL SDK for Mali, doesn't mean that a random Android device with Mali will have the drivers or kernel support in place, because that isn't something that Android requires.
Google has collaborated with Adobe in porting their OpenCL shaders to Vulkan.
If they actually cared, they would have made OpenCL available instead.