Please include article and authors name. It's okay to save money and use in-house people for voices. In house talent who are not actors or professional voice people will inevitably sound dead, take 10 times longer to record because of all the mistakes, and take longer to edit in post. Use a Hollywood casting agency or send your needs to talent agents who will supply you with just the right group to choose from. Agencies deal primarily with radio, TV, and largely with commercials.
Games have entirely different requirements.
All casting and talent agents have are headshots and cassettes that feature ads or narratives. Many don't know what their actors can do, nor are they expected to be good judges of great acting ability. They send out pics and tapes based on whose picture fits the description or whoever's tape they happen to have. Use celebrities to give your game notoriety and marquee value. This is like presuming that starving Ethiopians will be better nourished by rice boiled in Evian water.