Although there is no direct competition with Zerodium which is centralized while Hacken is decentralized, it is better to say that they could be partners but will compete on the black market.
Zerodium is large security company that currently running so it is too early to say that Hacken is better but HackenProof offers a lot features for white hat hackers and also encourage young but pomising hackers to join bug bounty of HackenProof (I don't know if Zerodium offers the same).
You could check it for yourself and compare the HackenProof to Zerodium features on their Whitepaper page 16.