The only way you can Special Summon this card is via its own procedure.
"Dark Armed Dragon" can still be Special Summoned while there are non-DARK monsters in your GY.
The effect of "Dark Armed Dragon" that destroys 1 card is an Ignition Effect. Removing 1 DARK monster from play is a cost.
"Dark Armed Dragon" cannot be Special Summoned from the GY, even if it was properly Summoned beforehand.