Mixed race couple in the 20s accepted in a suburban area?

The city where the movie was set was never specifically stated but was said to have been based on the place where Walt Disney grew up which would have been in Missouri. In Missouri interracial marriage was not legal until 1967... which is also when it was made legal in New Orleans. So it really doesn't matter which place it was set in it was illegal.

As for your example of Creole people, a Creole isn't necessarily a mixed race person the word was used for people born in Louisiana rather than someone born outside the area. Now there were lots of Creole people that were of mixed race, black and some other race... however in the south a person that was in any part black was considered black from a legal aspect, the so called one drop rule. So a Creole person may have been technically a mixed race person but from a legal standpoint they were black. In short Creole wasn't a pure racial designation and was more akin to the term carpetbagger which simply applied to someone in the south that was from the northern states. Simply because the majority of Creoles were mixed race didn't mean they all were.