Who should get credit for a song?

So, I'm sure by now most people would've heard of the musician Avicii. Well, can you tell me anyone (other than Aloe Black, that's fairly commonly known I think) who is singing on Avicii's songs?

Exactly (Well, assuming you couldn't), how do we know who to give credit to if we don't actually know who is doing it? I love the vocals of the person who sung on Hey Brother and Addicted to You, and I had NO idea who they were until I actively looked up who did it.

Other DJs like Clavin Harris and Flume give credit by saying "Ft. ___", but some DJs don't bother to do this. What do you think, do DJs need to credit the vocalist or can they credit it as their own work?

Personally, I feel they need to give credit where credit is due. I would be so pissed if I did a collab with someone on anything and I wasn't credited as having some sort of influence.

 

http://www.chicagonow.com/music-mom/2014/02/does-avicii-sing-the-answer-isnt-as-obvious-as-you-would-think/

I found this, Aloe Blacc is only in two of his songs, Audra Mae is in three, so she is in more.