Performance hit with column alias
A view, being just a query persisted in the database, should not theoretically have any performance hit. Same is true for column or table aliases. The performance hit, if any, will be barely noticeable once the execution plan is compiled and cached by the database engine. So, there is no performance justification not to use column aliases based on views. Having said that, I second Aaron Bertrand that the application should not have been written in incorrect schema. I would fix the application just for the sake of best practices and not to "create a permanent messy layer of indirection" as Aaron Bertrand said.