I use Infernal Dragon quite often, but only to get rage, namely rage from killed summons of creatures like Chosha or Friendly Goblin Bastard. If there is such a creature in my battle, that means I'll never run out of mana and resurrect all guys easily
Dragon Level 1 is enough for that, but if I have mana I cast level 3, just to be safe.
Also I remember one battle against undead when only surviving units were my Infernal Dragon and his colleague, Ancient Phoenix. All my base units were completely destroyed. Since Dragon is extremely susceptible to poison it was Ancient Phoenix who was doing all the work (undeads are nasty), but Dragon was needed so I could cast second Phoenix after first one was killed.