First of all, sorry about your brother. Second, wallhacking is a reality in online gaming... I know that's sort of a cop out, like they can't make an anti-cheat or whatever, but... you may have no idea how HARD it is to prevent cheating. You can't write a checksum into the client; they'll just hack the client and remove the check. You can't encrypt the network protocol; they'll just decrypt it, and besides, that introduces a LOT of overhead (LAG). etc.
So yeah. It's really pointless to go after cheaters. It takes a LOT of effort which would be better spent improving other parts of the game. Jitspoe is working largely by himself on the paintball2 project, on a budget of exactly zero dollars.
But yes, it is true. There are cheaters in DP. But as Termin8oR says, they suck. It sucks, and there's nothing you can do about it. And I just wish everyone on this board would Get Over It.