Cause of dawn phenomenon?

Does the liver pump out glucose primarily as a response to low blood glucose or low insulin such as is seen in LADA?

Yes.

There are multiple phenomena possibly in play. There’s the ‘Smogyi Effect’ - which is essentially the result of the liver responding to an overnight low blood sugar and releasing glycogen to handle the situation - resulting in high numbers in the morning. This is not what is usually mean by ‘dawn phenomenon, (DP)’ however. Some beleive that DP is caused by the overnight fasting, and the liver respondsto assure there is enough glucose in the blood for brain function; however, DP is most likely a response to the natural cascade of hormones that are part of the waking process, such as cortisol. Depending on sleep patterns, etc., that can be mild or very significant. In and event, the presence of enough insulin in the blood stream can curtail the release - or at least allow the cells to absorb that glucose.