We don't have flash loans but even if we did there are so many ways this attack would not work on Hive. For example, DHF only pays out a maximum of 1% per day, and only 1/24 of that in a single payment. The most you could pull out with malicious voting is about 0.04%. But you can't even do that because you have to power up to vote, and it takes 12 weeks to power back down (making it impossible to repay a flash loan). And even then you don't even get to vote for 30 days after powering up.

It's amazing how these well-funded projects manage to get so much wrong compared to a no-external-funding community project (Hive).