First, I don't think it matters for the answer to your question whether the omniscient God is or is not the creator of the beings whose conduct He foresees. Thus suppose the rats are created not by God but by some fairy. God observes the rats and, knowing of each whether it is smart or dumb, foresees whether it will end up rewarded or punished. Can this new wrinkle in the story -- that the rats are created by some fairy rather than by God -- possibly make a difference to whether the rats have free will or not? I cannot see a reason for believing this.
(To be sure, the wrinkle makes a difference to God's responsibility: if He creates dumb rats Himself, then he is actively responsible for the suffering they predictably undergo in the punishment zone. If He's merely an onlooker, then He is at most passively responsible insofar as He could but fails to protect the dumb rats from pain.)
Second, I don't understand why there should be felt a tension between foreseeability by others and free will. The only way your conduct can be unforeseeable is for it to be indeterminate: ruled from moment to moment by quantum events, for example. Surely, that's not a good example of free will. On the contrary, I would think that good examples of your free will are quite predictable behaviors. Those who know you know certain things about your future behavior. They know, let's say, that you are deeply committed to stand by your sister. You have carefully thought about this commitment, fully embraced it, adjusted your other values and commitments to it, built your life around it. You and others assume that you could cut your sister loose if you so chose, but you and they (and she) know that you won't. Here the firmness of your commitment seems quite compatible with the freedom of your will (and others' foreknowledge is based on your commitment and not the other way around).
Returning briefly to the first point, suppose now that your firm commitment to your sister was part of a plan your mother hatched before giving birth to you. Knowing of her daughter's frailty, she deliberately had a second child who would stand by her first one. When you were old enough to understand, she explained all this to you and helped you appreciate the wonderful difference you could make to your sister's life. Your mother correctly foresaw that you would be moved by this appreciation and would become committed to standing by your sister. Again, I don't see how adding in this additional information about the history of your commitment to your sister undermines the initial judgment that your foreseeable loyalty to your sister is compatible with your free will.
The difficulty of the free-will problem seems to be not specific to certain scenarios (e.g., free will in a world with an omniscient creator god), but quite general: how to make sense of it at all.