If he's taking out a loan to pay off the overdraft this will show up on his bank statements and the ECO will probably think this is just as bad. the only way to to it with a loan is to use a different bank account, take out the loan, pay the monthly payments for the loan from a different bank account, then wait seven months until he has six monthy bank statements that show no overdraft, no statement showing an overdraft being paid off and of course no monthly payments for the loan that cleared the overdraft.
Some people also do this to show some savings in a savings account, if you borrow money and put it in one account, pay the monthly payments from a different current account so that the monthly payments do not show up on your normal current account and then add some money to that savings account each month, then it looks like he has enough money to pay all of his bills and still has enough to add to his savings each month. Again you would have to wait seven months so that he could show six monthly savings account statements without showing the initial (borrowed) money being paid in as the ECO would wonder where this initial deposit came from.
Iain.