I'm under the impression that you should have no reason to think like that. In a fair payout method, all shares should have the same expected payout, and not depend on history at all. With DGM (and most other methods as well), the actual payout per share will have lots of variance, but it should average out after a long enough time, even over multiple accounts that are mining only occasionally.

DGM is really hard to understand, and unlike with PPLNS, I still haven't grasped it well enough to be 100% sure of the above. However, it would be a very lousy payout method if miners were forced to stay on the pool to not lose their expected payouts.