I did actually think that Apple required the use of Apple's developer tools for iThing apps --- so unless you can compile your target language into C, C++, ObjC (or Swift, I suppose) and then use XCode to compile the final binary, your app would be rejected. Has this changed?
Yeah, but it's still producing native code via a non-Apple toolchain. I'd want to check the T&Cs carefully, in case Apple notice and pull the app further down the line.