When someone gives you their account email and password, you will have full access to their account and can transfer funds to that account using other methods. So why would anyone give you access to their account with their funds?
Well I assume you are an honest person. And I also accept your condition that you will gamble using my funds and account and i should pay you 50% of my total profit. But if you lose my funds while gambling then who will take the responsibility of that money? Will you take responsibility for 50% of that lost money? As you are ready to take 50% dividend ?
He didn't say that you will need a balance once you handed your account to him but if it works the way you describe it, of course it was your own responsibility in case he loses your money because you accept his conditions anyway but I think the commission will now change.
It won't be 50 over 50 anymore but his share is going to be lower than yours. I think in order to perform this, we will be needing him to record his gameplay live so that we will see all of his actions and we are sure that he won't lie to us that he didn't win so that he can get all the money. He can also create his own account but I wonder why need to use someone else account?