Do your blennies look anything like this, ej?
This particular one was collected in the Gulf and is supposedly a Mollie Miller blenny. "She" has tons of spots on her, around the mouth and gills especially, that make her look like she is breaking out with parasites. So long as the spots are bilateral I think you are ok. Even if it is a solo spot, I wouldn't be too concerned unless it stopped eating. Mine scared me badly a few weeks ago and was fine after a few days. I am so glad I didn't tear the tank down trying to get a QT started.
As for what they eat, mine is a huge pig. It loves nori - so much that it rides it like a magic carpet on the clip, but it also eats Form 2 flake, mysis and cylopeeze now. It has the most character in my tank and is almost like a dog begging for attention.