For the sake of discussion, would a 1GH or 2GH miner even be able to find a block on ckpool against all the few hundred GH and TH there?
Yes any submitted hash at current diff can odds are low but possible
Does the difficulty of work that ckpool sends depend on my miners hash rate or does the pool not discriminate?
That is, do I get the same shot at high (or current) diff shares with a 2GH miner as a high hash rate miner?
Will the pool even send useful work to a 2GH miner?
Difficulty is just an arbitrary way of describing the work you're doing. It doesn't make your mining hardware work any harder, less hard, more efficient, less efficient or anything like that. With solo mining it's purely used for your own feedback purposes to know your hardware is hashing and regardless of what diff you end up seeing, your chances of solving a block and finding a high diff share are once again proportional to your overall hashrate. Solo ckpool chooses a diff over time that gives you a reasonably accurate hashrate estimate and nothing else. Everyone starts at the same diff and then the pool adjusts accordingly.