not quite; for starters the usual scenario of a prediction market on someone's death is a public question that doesn't have any "exclusivity", as opposed to the situation where some hitman gets paid in advance, or the movie trope [e.g. in John Wick] where there's a bounty and the potential killers compete over it... my point is that in these prediction markets, insiders signal their info to the public, and anyone can hedge.

tl;dr prediction markets are not an efficient way to pay for murder, similarly to how blockchains are not an efficient replacement for a database