First of all, I would like to say this: The bet system only applies to spectators. Players that are still in the game are not able to bet on other players, just like you can't bounty someone while being in a game yourself.
Regarding the hackers: hackers have the same chance at winning or losing the bet as much as other players. Hackers only have an "advantage" over other players in game, they can't use their hacks anymore to kill players once they died.
Regarding the targeting: the same as above. You can only bet on people if you join a game that has already started or after you died in a game yourself.
I hope that this made sense...