Yes that is fine for that actual operation of producing a file but it looks identical to if they were white spaces.
That is true, a white space does look like a white space, but irrelevant to the situation.
The IDE adds two spaces regardless of position. To keep vertical columns aligned in the IDE you may be required to either remove or add white space, especially when say formatting lists of array values when they contain an uneven length. Whereas a tab structure would align to the tab boundaries.
Of course you can make them look identical, however one way is simple the other is a pain in the ass. Which is why I use notepad++ for everything apart from the sketch file.
I use notepad++ sometimes for edition. It produces real tabs. Arduino 2-space fake tab annoys me only when I start editing arduino code outside the arduino IDE. Nothing lines up and all my comments are screwed up like some kids typed them. This may be a Processing problem, which is the host of the Arduino IDE, i.e. a modified Processing IDE. Seriously if your screen isn't wide enough for a 4-width(not space) tab, get a new one!
The two space tab may be madness, but I believe method was involved. The IDE has a feature we all dislike called 'copy for forum'.
On the forum, tabs proved a problem, some browsers draw tabs using up to 8 or 10 characters. Others use a CSS property that is set using relative coordinates ( and can be quite large also ). By using two spaces instead of a tab, the webpage looks a lot cleaner ( usually doesn't require horizontal scrolling ). Sometimes when I post code written outside of the IDE, I will replace all tabs with two spaces, just so it fits better. Notepad++ allows macros which makes the conversion to and from tabs a single click.