Finding someone’s name in the credits already tells you that they can’t be ghost producers of that song.
You are not a ghost producer if you were only involved in the engineering (mixdown/master). You were an engineer.
You are not a ghost producer if you weren’t named as an artist but were properly credited for your production contributions. You were either the producer or a co-producer.
You are not a ghost producer of a full song (with vocals) if your control of the song’s direction ended after you delivered the instrumental. You were the beatmaker.
You are not a ghost producer if you did the arrangement, created a lead sound, did vocal recording or composing, but still had no influence on the song’s direction because someone intensively guided you through the process of the song’s creation, making sure everything went according to how he/she wanted. You were the arranger, audio designer or composer.
You are a ghost producer if you produced a song and let someone else take credit for your part.
Read the full article here: http://edm.com/blog/ghost-producer