is adobe reader safe to use on a mac?

Yes, Adobe Reader is safe to use. Download it directly from the Adobe site at http://get.adobe.com/reader/ .

There was recently some malware that involved Adobe Flash, however, that has nothing to do with the Reader.

Specifically, if you see any dialog involing getting Adobe, and you are not visiting an Adobe website, it likely is a problem with the website you visited, and someone has hacked it to try and get you to click something. Only download Adobe software from their website.