I vouch for USA because of Black Crow, Dragoon, Daydreamer, and Hard Boiled. The clothes Daydreamer and Dragoon wears seem reminiscent of the American civil war, and Daydreamer's epitaph and a mortal description in Spooky Hallow confirms this takes place in America. Hard Boiled's epitaph makes reference to Colonel Sanders, an American fast food figure. The inconsistencies are from the cultural divide of the UK team making a game set in the USA in the days before internet speed and search engines were so fast and easy.
This is correct. The mission was known as The Uninvited. It was going to be based on a city block with a sleazy hotel and other buildings. The concept art labels a building on the map "New Orleans" style architecture and "Southern America". This mission may have been cut for this exact reason because the developers wanted a generic American town based on many horror and pop culture references.