The "double geometric" payout method as used on the Ozco.in pool is supposed to be fair and prevent pool hopping, but is this method fair to miners that only mine for a few hours per day, as opposed to miners that mine 24/7?
Yes. If you mine at a given point in time, you do not know when a block will be found, and thus your reward for shares you submit is a random variable. DGM is constructed so that the average reward for a submitted share is always equal to what you would get from it in PPS (assuming equal fees). The total reward for all shares you submit is additive - so it follows that the average reward you get in DGM is equal to what you would get in PPS, no matter what is your mining pattern.
However, the reward you will get is random and has some variance, and the variance is greater if your mining is intermittent. The exact degree of this depends on the parameters used by the pool.
More background information about mining pool reward methods can be found in Analysis of Bitcoin Pooled Mining Reward Systems.
As far as I know, yes. The expected value (in BTC) of a share is constant in time, for a given difficulty/pool-hashrate/etc.
If you are only mining a few hours a day, this will not likely work for you.
The way DGM works is that at the start of a new block all miners start to gain credit for the block. All miners will gain a cut. For instants when I mine with 1.6 GH in a pool with about 1.8 TH I'll receive 0.043xxx BTC when the block is solved. If the block takes 5 minutes I get that for 5 minutes work. If it takes 5 hours then I have to work for 5 hours. Over time this averages out so long runs and short runs are inconsequential. However if you mine on a 5 hour block for only 2 hours then your reward is going to be substantially lower.
Another point worth mentioning. On many pools your award is not paid until the block is confirmed. This usually takes about a day.
My recommendation is to use a PPS Pool if you are going to only be mining from time to time.
I find it interesting that the creator of DGM is here, claiming user statements are incorrect. As with any "hop-proof" payout schema...
It has the net effect of punishing miners who don't mine for an entire round. DGM greatly reduced the risk to the pool op by transferring those losses to the miners. PPS is exactly the opposite, pool ops take all the risk & variance instead of miners.
DGM is for pool ops who can't manage their business well enough to keep correct reserves. Miners will quickly find their earnings decreased and start looking for other more favorable payout schemas.