Is it reasonable to evaluate spelling/grammar in reports for students diagnosed with dyslexia? Students diagnosed with dyslexia qualify for accommodations at most universities. As with other special needs students, they're entitled extra time for work, exams, access or licenses to spell checkers, etc. 

If these accommodations are in place, and assuming good grammar/spelling is part of the evaluation of work outlined in the university course syllabus, is it reasonable for an instructor to penalize students with dyslexia for making spelling/grammar mistakes as with other students?
I’ll go for a legal answer, at least valid in my current place of employment (France): dyslexia, which must be medically characterized as a learning disability for an individual, is covered by the laws regarding disabilities. As such, students impacted can request that exam conditions be modified for their benefit: most commonly by giving them additional time to “compensate” for their disability, but it could also include changes in setup (such as having access to a dictionary, spellchecker, or even a secretary). On the other hand, no leniency should then be granted on judging the exam paper.

The operating principle in all cases should be that of equal opportunity. (See here a summary of jurisprudence by the Association lyonnaise de droit administratif.)