They sure didn't look Klingon at first, but assuming the 'sarcophagus' is full of ancient "proto-Klingons" from millennia ago, it could work.
IF the leaked "Klingon Picture" turns out to actually show Klingons- then I'm going with your theory. That they're proto-Klingons awakened from cryogenic sleep/stasis/whatever.
And this falls in line with the "no reliance on time travel for season 1" comment.
A sleeper ship definitely isn't technically time travel.