In answer to your first question, it depends on the rationale, or reason(s) behind the translation exercise. Effective teachers ask, "How will my students benefit from this exercise?"
In answer to your second question, CDs are beneficial because they offer students opportunity and exposure to hear and therefore process different idiolects and dialects. However, if the only exposure they have had is the teacher's voice, then using a CD in an exam wouldn't be fair to them. If they have had exposure, it's a good idea to check the CD's quality and speech rate before deciding to use it. It's a good and trusted measure in setting your students up for success.
- For Teachers