Could the wetted Li boiling actually cause a "precipitation" of the H- onto the Ni surface?
After giving a bit more thought to this: boiling can generally remove a large fraction of gases dissolved in liquids. This should occur with metals too, although their behavior with gas solubility is different than liquids like water.
I've found the graph below which shows the solubility of hydrogen in Al over a wide temperature range at atmospheric pressure. It increases until somewhere below the boiling point, then it markedly drops. Li may behave similarly assuming that some H remains in solution after all the LiH is decomposed, but I don't know if it would precipitate out directly as H-.