Dortmund is not a strong challenger and they always fail to be the best even though the hope to get success is in sight. The Dortmund group phase managed to escape but I am not sure they can go further because their appearance is sometimes less consistent. Moreover, the Champions League is very competitive and very different from the domestic league, so the competition here will be far more difficult than in the domestic league.
Dortmund are not good enough to win titles in Bundesliga and Champions League recent seasons but they have good quality. They performed well in their group to be two eligible clubs and it shows their quality. PSV looks to be an opponent that does not outweighs Dortmund in quality and the first match shows it too. They are the host but only can equalize the match by a penalty and will face with big risk at Dortmund's home stadium.
A draw at home to PSV Eindhoven is indeed very beneficial for Dortmund because in the second leg they can pursue goals at home. If you look at the opportunity in the match Dortmund should be able to score more than one goal but not put to good use. PSV Eindhoven managed to master the game and dominated the match better than Dortmund but unfortunately unable to add goals.
Dominate a match at home and fail to get a win, it's a disadvantage of PSV before a second match in Germany. Dortmund actually achieved their target when playing in Netherlands and they will return home with a little advantage. It is not too much as if Dortmund lose at their home stadium, they will be knocked out by PSV. PSV don't need any big win, just a minimal win and because Dortmund also need a win to go next, PSV can play defensive and counter attacking in a next match. Dortmund must know that they have small advantage but also have risk to be lost in this pair.