Hi,

Is there an official answer ehether the Overlord draws a card after defeating someone treated as a hero? e.g. Celia from 'The Incident' quest from Nerekhall?

Thank you

There is. He does not. Furthermore, "bloodlust" only works on characters for which he would already draw a card for defeating (that is, ONLY the core party of heroes. No allies, no familiars, no NPCs.)