Do enlighted people cry? Did the Buddha ever cry? What is the Buddhist view on crying? I don't remember hearing or reading about the Buddha ever crying. Is crying a consequence of "lack of understanding" of the ultimate reality?
Crying can be caused due to both physical and mental reasons.
Physical reasons:

Irritation in the eyes.
Sickness affecting the eyes.
Side effects of strong medication or extremely spicy food.

Mental reasons:

Sadness(obvious sadness and the sadness disguised as compassion), depression, aversion to pain, fear
Clinging to happy/pleasant/joyful states of the mind.

Assuming that this question is aimed at the 2nd category, it is highly unlikely that a fully enlightened being would cry as they no longer become sad or cling to pleasant states of the mind.
Arhanths only have Kiriya Cittas. Those are of 3 types.
i. Consciousness turning to impressions at the five doors
(panca dvara-avajjana) accompanied by feeling of indifference(Upekkhā).
ii. Consciousness turning to impressions at the mind-door
(mana dvara-avajjana) accompanied by feeling of indifference(Upekkhā).
iii. Consciousness of the genesis of smile (hasitoppada
citta) accompanied by joy(Pīti).
Hasita(a smile which slightly reveals the tips of the teeth) is their reaction to joy. If they ever cried, there should be another called the Assuppada citta. But there isn't! :)