Yes it uses the same keys.
Is this a new development. I asked the question of Fluffypony and he said no a week ago:
Quick question. I see under account details you can get address, view key and spend key. Would it be possible to also get the seed words used for the "restore deterministic wallet." That way, if there was ever a glitch with the website, you could quickly replicate the entire wallet to a local machine.
Right now there isn't interioerability between simplewallet and MyMonero. We will be providing that capability later on.
https://bitcointalksearch.org/topic/m.9654716