Gee, have I been asleep at the wheel...
It is possible to determine if there is a meteoritic content with a minimally destructive test. The issue is finding an Electron Microprobe...
The surface must have a very small area polished (that is the destructiveness of the test). The Electron Microprobe will determine what elements are available. Earth surface rocks do not have the same availability of trace elements as meteorites. The trace elements are the fingerprint used to identify cosmic materials. Therefore, even if there is only one percent meteoritic material in the metal, it is still possible to tell if meteoritic material is present or not.
If there is only a small percentage of meteoritic material in a Keris, then looking at Ni content alone will not be an indicator of cosmic origin since the majority of Ni is not from the meteorite itself. Therefore, short of testing, there really is no way to know if a Keris has meteoritic material in it.
Great article Rick!