Abilities like shoot through are not "hits" so i assume the monsters do not get defense. However, the XP is given per hit and wound. So does the D6 damage not give the hit XP but you still get the +5 per wound?
LavaMen have a range value. Does this mean that they do not move to base the heroes? Do they automatically have the range attack listed at the bottom of their card or is that just for the upgrade ability? That ability says they get an additional shot every round so it makes me think they get a normal shot every round, but it is written weird.
1) Defense applies to anything that does damage to an Enemy unless it states otherwise.
2) It has been mentioned somewhere online that for the purposes of XP, there is a theoretical 'hit'. Personally, my group does not do this.
3) Enemies always move to engage into melee unless they have rules that state otherwise. For example, some Enemies have the ability "Shootout", or the Ability "Retreat".
4) Specifically to Lavamen, they only get the ranged attack if that Elite ability is rolled. What the text says is that the Lavamen get the ranged attack each turn before they take their normal turn. The normal turn, which is to move into melee range and make a melee attack. It is very similar to the Assault ability.