Using other people's data for dissertation: ethical or not?
Unless the student claims that they collects the data himself/herself. I do not see any scientific misconduct in using other people's data with their permission. 

Of course collecting good data is a contribution. However, even if the student collects data themselves, I would be very surprised if that is more than 30% of the contribution in their thesis.

TL;DR: No big deal. That might be a bad professor, but it doesn't mean everything he does is wrong.