As someone involved in the hiring of engineers that must have experience using NDK (I work for Unity and support the VR/graphics groups), I see quite a few resumes of people who claim to be using NDK and c++ but at the same time reference the use of JNI. I thought JNI basically made it possible to use NDK using java without using c++. Any thoughts? ( I know I am a recruiter but I am not using stack overflow to recruit, rather, better understand the very technologies I am working around every day. I appreciate your help in advance )
Hiring is difficult. I commend that you are taking the extra step to familiarize yourself with these sorts of software engineering details.
As you observed, the two languages aren't interchangeable. However, knowing JNI doesn't preclude experience with NDK, or vice-versa. In fact, it might be preferable to note applicants that are familiar with both. For instance, most high level language programmers don't strictly need knowledge of assembly level programming, but those who do may be more versatile. Having some awareness of what happens outside your required knowledge domain can give you insight toward performing better inside your knowledge domain.
Ultimately, if NDK experience is 'must have' requirement, advertise accordingly. Some of job seekers fear aggressive keyword filters & tend toward over inclusion in an attempt to avoid being screened out. On the other hand, some applicants get real loose with the truth in an attempt to get in the door. Clearly signalling the job requirements (I.E. 'must have NDK experience') is probably the best way to avoid losing qualified candidates. After that, advertising time/space/$ permits, stating that 'JNI by itself is not sufficient' may help focus your candidate pool.