Not necessarily, for instance in the characters in that screenshot the main transparent shape is a blue to yellow gradient and I believe it's set to overlay. So it's a combination of blends and gradients and transparencies. I for one am using blends there where a normal (radial or linear) gradient does not accentuate the shape enough. Another trick would be combining more gradients in a single shape using the appearance palette. You can get some neat effects that way too.