I hear there is a biology professor who won't write recommendations for creationist students. I wanted to comment in general:
If I ask Joe Dirt to write a recommendation letter for me, he is perfectly right to refuse. People needn't write letters for anyone they don't want to.
However, in a school setting, students are required to have these letters. And professors are expected to write them. Refusing to write students a letter hurts them. And such a blanket refusal is morally wrong.
Refusing letters over a student holding some theory, only makes sense if the theory directly interferes with the student's studies, and makes her/him significantly (meaning "enough to matter" not "lots") worse at them. This basically means refusing letters for incompetence (math major who thinks 2+2=5; politics major who thinks "democrat" is a type of fish).
So what about biology and creationism? Well, if you want to be a doctor, you learn how human beings are, and about medicine, and it doesn't matter. If you want to be a vet, and you disagree about why vestigial organs exist, but know the same facts about them, it again doesn't really matter. If you want to be a zoologist, and study the evolution of animals, it does matter.
So my view is, to be moral, the biology professor must refuse recommendations on a case by case basis, and only in very specific circumstances will refusal for belief in creationism be acceptable.