You may very well be right, and your explanation as to how the image functions in relation to the knife's possible function and its representation of the power to overcome evil makes a lot of sense. But of course, Hanuman also would embody that same power.

However, we're back again with a problem relating to the bull-like figure on the knife, which, if the monkey is Vali, would have to be Torapi, the demon buffalo whom he kills. But on the knife, this is definitely not a buffalo (unlike the modern statue that Nishedha showed us). So we're back again with a puzzle, though a different one! And the monkey really does seem to be nibbling on it quite happily, not fighting it.

Also, there are actually many, many representations of crowned Hanumans in Angkor-era sculpture, especially the bronzes. Almost all divine beings are portrayed by the Khmers as bejewelled and crowned, regardless of whether they were "royal." The most frequent representation of Vali actually is in his death - a tragic and disquieting moment because he is killed by Rama. Hanuman, on the other hand is always shown triumphantly alive, frequently as a figure on the head of ceremonial battle standards. Here (attached) is one example; there are several others in Emma Bunker's beautiful book Adoration and Glory: the Golden Age of Khmer Art, published by Riverbooks in Bangkok.

But in deference to your interpretation, I'm going to refer to the monkey on the knife as "Vali or Hanuman with the Head of a Bull." That seems to cover the different bases.

All the best,

Will