Unity permite detectar eventos de mouse o puntero sobre elementos UI.

Interfaces comunes

Necesita:

using UnityEngine.EventSystems;

Ejemplos:

IPointerEnterHandler
IPointerExitHandler
IPointerClickHandler
IPointerDownHandler
IPointerUpHandler

Hover

public class HoverUI :
    MonoBehaviour,
    IPointerEnterHandler,
    IPointerExitHandler
{
    public void OnPointerEnter(
        PointerEventData eventData)
    {
        Debug.Log("Entró");
    }

    public void OnPointerExit(
        PointerEventData eventData)
    {
        Debug.Log("Salió");
    }
}

Click

public void OnPointerClick(
    PointerEventData eventData)
{
    Debug.Log("Click");
}

Usos