I cannot answer the question.
I do not know the qualifications of your contractor, nor do I know how he is planning to do the installation. You need to find out if he is qualified..... Also, make sure he is licensed and insured. You may need to get a permit so check with your local codes department.
BTW, I have also cut and braced a ceiling joist when installing a skylight in my family room. Ceiling joists are often cut when installing skylights too...... I am not the only one to do this!