No way. It's not safe at all. It's tied to Bitfinex -- they are owned by the same company. So Tether is subject to the same third party risk as Bitfinex. Indeed the terms are scary. Technically, your USDT is not redeemable for anything. In practice, you can't redeem it for real money either because Bitfinex/Tether does not have any fiat banking capabilities right now. I would not be comfortable holding USDT for long at all.
And no, Poloniex/Bittrex/Kraken/etc definitely won't honor your USD value if Tether goes down in flames. That's why they either don't have USD deposits/withdrawals, or they keep USDT as its own market (like Kraken).