Update: I got 3 280x Powercolor cards, seeing 5.1 MH/s on the miner but the HR on the pool is fluctuating a lot.
It's a crude conversion of normal sgminer just so that it can play with the darkcoin hashing algorithms. The conversion apparently produced quite a few bugs especially in the reporting aspect of the program ("null", "0" difficulty, no A: diff etc). So you are not doing something wrong, it's just the way the program works.
Thanks Alex! That's a relief. Just one other question - my DRKs have been unconfirmed on the main pool for about an hour. I know it needs 120 confirmations, but how long does that normally take?
I would estimate around 5 hours based on 120 blocks x 2.5minutes = 300minutes.