Hair in your face will cause pimples if your hair is oily or dirty. Hair is naturally oily, so that can be a problem. The oil clogs pores and causes pimples.
PROTIP: Use Head & Shoulders shampoo (not the generic).
It contains an ingredient (besides the anti-dandruff) that will get rid of the oil in your hair and prevent it from causing pimples. I believe Selsun Blue is the other shampoo that does the same thing, but I can't remember for certain, so don't bet on it.
I've been using Head and Shoulders for my hair for the past two years, and my hair looks healthy. But I don't think it would affect the pimples on your face all that much ._. Cause it never did for me.