Can Impermanent Loss Be Positive, Resulting in an Impermanent Gain?

No, impermanent loss is strictly a measure of opportunity cost, defined as the difference between the value of HODLing the initial assets and the value of the LP tokens. Since the AMM formula forces the pool to hold fewer units of the asset that appreciates more, the value of the LP tokens will always be equal to or less than the HODL value.

Therefore, the divergence is always a "loss" relative to the HODL strategy, not a gain.