But the hash they get from mp is just the salted serverseed and without the help of mp, appowner has no clue about its real value. So he does not know if it would make the player win or lose, which makes that option useless for cheating no ?
And if the hash doesnt fit to the one used in the bet which goes trough, then the bet wont be verified I guess ?

I'm not sure if the apps actually even check if the hash fits to the seed used in the bet tho :S

So if theres a cookie stored in browser with a hash and the cookie gets for whatever reason changed. Does mp check the cookie when the user sends the betdata to the server ?

I'd guess they do, so with a malicious cookie the bet wouldnd go trough = hasherror ?