General rule = the less alike 2 fish are, the more likely they will get along.
Gobies and Blennies, as far as I know, are pretty similar. They both chill on the bottom or rest on rocks, they both have long, slender bodies and like "caves" as a home. Not too sure how much a part coloring plays though.
Basically, if it doesn't look like anything else you have in there, you'll probably get away with it.
I have yellow watchman and LMB in 75 for a little more than a month - no
problems at all. YWG sits in his cave (or near by) all day long and comes
up only for feeding. LMB hops around from rock rock.