The DAO pays out only so much per day, so the bad proposal needs sustained funding. This could happen on a smaller scale with the DAO, as there is far less HP needed to sway votes. It would make for some ruckus, that's for sure, and whoever was lending that HP could kiss their reps goodbye. However, to those that wouldn't care about their reps, just the returns, it would be an interesting attack vector. The defense would be everyone voting on the returned proposal; thus, the attacker would have to pay rent on HP they couldn't utilize in the way they wanted. Would be an interesting attack for sure.