I seem to have misunderstood some of the rules regarding the sacrifice of Fire Imps on the inn.
"Burning down the inn: Once per turn, when activating his fire Imps, the overlord may perform a special action with a fire Imp that is on the Inn. That fire Imp is immediately defeated and the overlord places 1 fatigue token in his play area."
This allows the overlord to sacrifice a fire Imp during its activation as long as it is one the Inn? So it is indeed possible to reach the inn with a Imp and sacrifice the same imp in same turn?