Yes, the x86 system image can run ARM code. Note that the speed will be much faster than running a full ARM emulated system image because only the guest userspace bits need to be translated from ARM to x86. System calls are still marshalled to x86 calls, so memory accesses are many many times faster because (there's no need to drop into emulating the MMU).
(Also AFAIK illegal instructions are still validated and trapped as SIGILL or SIGSEGV)
(Also AFAIK illegal instructions are still validated and trapped as SIGILL or SIGSEGV)