< Do you know of any other program existing that puts up a warning for that?

in Sketchup you can't create a component if a previus name exist ;) so alert message !
you can create groups with the same name ;)

I understand your point of view, solution to see the up side corner can be a solution
but in very big project seems that can be helpful to be warned

a little trick will be not to make a message but just change the color of the text during the typing ;)
Normal color if any previus name exists, red color... (or bold ) if it's exact name at the end of type
So your are warned and can accept or not (add a letter or change it) the input by Enter without message needed ;)

PS And about the enligting of name selected on the browser? (see previous image)