Unusual Line in the Petrov

The main line in the Petrov's Defense is 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4.  - MCO 15th Edition, Nick de Firmian

What about this, after 5...d5, 6.c4 Bb4+ ? Good for White or good for Black?

You won't find Bb4+ in Game Explorer, but you will find 96 games after 6.c4 and 46 games after 6...Bb4+ in ChessBase.

In chess opening jargon, would this be called a sideline or something else, like a novelty?

Does the Rybka 4 Book by Jiri Dufek or Nunn's Chess Openings cover this line?

Thanks.

Here's one example. 

Here's a more recent example - 2010.

* Bump *

Is this too hard of a question? Perhaps I posted too late in the evening?

What's your opinion on this line ? What do you think are the advantages and drawbacks compared to the main line (6.Bd3)

I think 6.c4 makes Black's task of drawing the game easier. Attacking forces are flying off the board.

Here's the highest rated game in ChessBase with (6.Bd3). Black didn't get the half point.

c4 does come later most of the time. I googled this early c4 move and found nothing written about it.

I think the consensus is the early c4 isn't recommended -- 6.Bd3 is better, with an  c4 coming after 0-0.  In the even of 6.c4 is Bb4+ a good response.  -- It appears to be, yes.  I don't know if this line is covered in any books... if the analysis of it is as simple as we have it here, it would be called a minor sideline. It's the kind of thing opening books generally can't be comprehensive about without being very cumbersome.

I think the reason c4 isn't good for white is that after Bb4, black forces the knight to d2 (after Bd2 Bxd2 Nxd2), where in fact it wants to be on Nc3 after having played c4. c4 + Nc3 usually want to be together.

This is my uneducated guess and might be completely wrong.

Good point. c4 + Nc3 looks more helpful for White.