Adamantine has actually been demonstrated to not be immune to dragonfire, though it takes a lot of it to melt it - go into Arena mode, spawn a Blizzard Man (which will itself never die to dragonfire) wearing adamantine armor, then spawn at least a dozen dragons to toast it to cinders (but make sure they can't actually reach it) and the armor will eventually melt.
No. All you've demonstrated is that dragonfire ignites blizzard men, and furiously burning blizzard men melt adamantine armor. The dragonfire itself did not melt any adamantine.
Don't believe me? Try your test again with a non-flammable target:
[CREATURE:ELEMENTMAN_SLADE]
[DESCRIPTION:Living stone in the shape of a man. These strange creatures are found deep underground.]
[NAME:slade man:slade men:slade man]
[CASTE_NAME:slade man:slade men:slade man]
[CREATURE_TILE:'M'][COLOR:0:0:1]
[LIKES_FIGHTING]
[LARGE_ROAMING]
[BIOME:SUBTERRANEAN_CHASM]
[UNDERGROUND_DEPTH:3:3]
[FREQUENCY:1]
[POPULATION_NUMBER:15:30]
[NOPAIN][EXTRAVISION][NOBREATHE][NOSTUN][NONAUSEA][NOEMOTION]
[NOTHOUGHT][NOEXERT]
[NO_DIZZINESS]
[NO_FEVERS]
[BUILDINGDESTROYER:2]
[LARGE_PREDATOR]
[NO_DRINK][NO_EAT][NO_SLEEP]
[NOT_LIVING][EQUIPS]
[CANOPENDOORS][CAN_LEARN][SLOW_LEARNER]
[NOT_BUTCHERABLE]
[NOFEAR]
[PREFSTRING:impossible mass]
[NOBONES]
[BODY:HUMANOID_SIMPLE]
[NO_THOUGHT_CENTER_FOR_MOVEMENT]
[TISSUE:ROCK]
[TISSUE_NAME:slade:NP]
[TISSUE_MATERIAL:INORGANIC:SLADE]
[MUSCULAR]
[FUNCTIONAL]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:ALL:ROCK]
[BODY_SIZE:0:0:70000]
[BODY_APPEARANCE_MODIFIER:HEIGHT:90:95:98:100:102:105:110]
[BODY_APPEARANCE_MODIFIER:BROADNESS:90:95:98:100:102:105:110]
[ATTACK:PUNCH:BODYPART:BY_TYPE:GRASP]
[ATTACK_SKILL:GRASP_STRIKE]
[ATTACK_VERB:punch:punches]
[ATTACK_CONTACT_PERC:100]
[ATTACK_FLAG_WITH]
[ATTACK_PRIORITY:MAIN]
[ATTACK:KICK:BODYPART:BY_TYPE:STANCE]
[ATTACK_SKILL:STANCE_STRIKE]
[ATTACK_VERB:kick:kicks]
[ATTACK_CONTACT_PERC:100]
[ATTACK_FLAG_WITH]
[ATTACK_PRIORITY:SECOND]
[ITEMCORPSE:BOULDER:NO_SUBTYPE:INORGANIC:SLADE]
[ALL_ACTIVE]
Apparently it is an exception to the metal rule which is rather odd.
No, the other metals will all melt as well, IF they are loose items like the chain.
No. In v0.34, metals don't melt in dragonfire, including loose items, buildings, etc. It's a bug I've tested extensively. Try it yourself--you can set up as many dragons as you want in the object testing arena.
I looked through the bug reports and didn't see any mentions of the dragon fire + metal bug but I'm not sure if the "known" bug list I went through was comprehensive or not. Does anybody know if this has ever been formally brought to Toady's attention?
I discovered this bug, and, judging by the amount of resistance I've received, it is not a commonly-known issue. Feel free to create an official bug report if you would like.