I feel I should step in here and say that the "sharing" of DLC is officially frowned upon by Harmonix as they have relayed a few times on the official message boards. Sony's opinion is a bit mixed. Some people have posted how it may be a violation of the terms of service while others have posted quotes from Sony employees that seem to view it as acceptable (not specifically referring to Rock Band though).
Just be advised that it is currently a hazy legal grey area.
Also realize that unless you share a sub-account you'll have your credit card information in the account and anyone you share it with can make purchases. They could also, for that matter, change all the login and password information and lock you out of it. They especially might do this while keeping the credit card information intact. For this reasons it's definitely not what I'd consider "safe".
Just be advised that it is currently a hazy legal grey area.
Also realize that unless you share a sub-account you'll have your credit card information in the account and anyone you share it with can make purchases. They could also, for that matter, change all the login and password information and lock you out of it. They especially might do this while keeping the credit card information intact. For this reasons it's definitely not what I'd consider "safe".