I'm sure Gish did the chemistry and biochemistry to get his degree (from Berkeley, I believe), and probably did very good work as a graduate student.
What peer-reviewed work has he published since then, is the real question. I'd be glad to give the man credit for any work he has done that has been published in referred journals - that's how scientific credibility works. As far as his rants about evolution, they really don't have much scientific relevance if they don't directly reflect actual accomplishments in science.
I am certainly not Dr. Gish's agent or apologist, but, his career does seem to include practical application of science. Whether or not that qualifies as "actual accomplishments in science" I don't know...but I think it is worth considering.