That Seminary teachers shouldn't be asked but for a different reason than you have.

If someone is asked to rate or comment on the qualification of an applicant for anything, he should focus on his specific involvement with that individual. When I Look to make a new hire, I want to know how a previous reference or recommender has interacted with that individual. I don't expect them to comment on College grades or other work experience. Tell me what you know about that person that no one else might know, and be honest and straightforward with me.

In the case of a seminary teacher, it is how that individual is as a seminary student. That's it. If a seminary teacher comments on any other things like grades or test scores or things that are completely outside of his interaction with the student, or if the seminary teacher takes those things into account for how he is evaluating that student for seminary, then yes the seminary teacher should not be involved. The seminary teacher does not need to comment on those things. They stand for themselves on separate parts of the application.