There's a difference between someone who genuinely believes what they are evangelizing, and paying marketing people to spread some corporate opinion. The OP is

There's a difference between someone who genuinely believes what they are evangelizing, and paying marketing people to spread some corporate opinion. The OP is referring to the second type I think. Of course the two are not mutually exclusive, you could have an evangelist job for an open source company selling data protection software/services for example.