This is different though, because of the “except with knowledge of said engineer” line. This code is trying to prevent clients from, for example, getting a “second opinion” on a project if they are unhappy that the first engineer deemed it unsafe. This isn’t really an issue in teaching. I think that it would be impolite to just drop in on a colleagues class unannounced, especially if it is a bit lecture where you might go unnoticed, but I don’t see why a prearranged visit would be unprofessional per se. (Perhaps because it would cause students to doubt the quality of their instructor?)

FWIW my understanding is that at my university the response to poor evals is a visit from a colleague, to assess whether the teacher really is weak or if the material is just difficult. Depending on that, the instructor may get additional coaching in teaching technique. This seems like a sensible approach to me.