Yep Hopping doesn't have to mean your gain is someone else's loss.
Maybe many think those two ideas are directly connected - but obviously in this case - they aren't.
What I guess DGM does is allow you to capitalise on the fact that when a pool is lucky, that luck extends beyond the time when it occurs
Thus you can get part of that luck after the fact.
Pool hopping at a proportional pool does mean that other lose. There's only 50btc per round, and if you are getting more than expected of that 50btc, then someone else is getting less.
The first two charts
here should give you an indication of just how much fulltime miners lose at a proportional pool if there are pool hoppers.
If by 'pool hopper' you mean someone without a share payment maximisation strategy - who bounces from pool to pool or round to round without regard to how many shares have been submitted for the round or what kind of scoring system is being used - then I think that 'intermittent miners' is a better name since 'pool hopper' has come to mean someone who has a maximisation strategy based on using pools with broken payout systems.