This makes no sense to me at all.

Surely the DRK/BTC price will keep the same ratio as the BTC/USD price in relation to the DRK/USD price.

Meaning you wouldn't get BTC/USD and DRK/USD dropping and DRK/BTC rising. They are all in sync with one another.

Otherwise you'd be able to a ton of cash trading the differences, which I'm assuming isn't possible.

So essentially monitoring the DRK/BTC price is the same as monitoring the USD ratio equivalent