Serious question for Kraken-Septimus: is it safe to assume that, like Bitstamp, Kraken is backed by (supposedly) real USD/EUR, and not USDT?

Couldn't find the answer anywhere. I would assume that if, like Bitfinex or Bittrex, Kraken's USD was actually USDT, Kraken wouldn't provide USDT/USD pair for trading. So I'm assuming that Kraken only provides USDT for quick transfer between exchanges, but does not rely on it more than that, and that by holding USD or EUR on Kraken, we aren't actually holding USDT/EURT. Do you confirm?