I've killed Genki twice using the knifethrower from GAT V dlc, using 50x spawn. I did not get money for either kill :/
This has happened to me a lot. After observing the last few times it's happened, it seems as if the cache symbol sometimes falls through the ground when Genki dies, making it impossible to pick up. Probably a clipping issue with the game engine. The health pickups don't have this problem since they float above the ground instead.
<Cash>
<Min>100000</Min>
<Max>100000</Max>
<Dollar>
<Min>100000</Min>
<Max>100000</Max>
</Dollar>
</Cash>