It seems counter intuitive to me. It seems you're saying that static analysis cannot reach every branch of the program (and thus its underlying system libraries).
I'm surely missing something and would be grateful to anyone helping me out!
You could provide hints for these circumstances, or change a program to work differently to avoid the practice, but having library resolution delayed until runtime and until after the program has started is a real thing.
That is, let's say syscall 1 is definitely used, syscall 2 is definitely not used, whether syscall 3 is used depends on halting problem. Including only 1 and 3 to unikernel is safe and better than including all of 1, 2, 3.