Yes it is safe if you only download direct from Adobe.
Download Adobe Flash Player for Mac to view Flash content in your Web browser. Adobe Flash Player has had 4 updates within the past 6 months. Adobe Flash will be going away soon, but for now, you can easily install and enable Adobe Flash Player on a Mac computer using a Safari browser.
You can check here: http://www.adobe.com/products/flash/about/ to see which version you should install for your Mac and OS.
You should first uninstall any previous version of Flash Player, using the uninstaller from here (make sure you use the correct one!):
and also that you follow the instructions closely, such as closing ALL applications (including Safari) first before installing. You must also carry out a permission repair after installing anything from Adobe.
Adobe Flash Player Mac Download
After installing, reboot your Mac and relaunch Safari, then in Safari Preferences/Security enable ‘Allow Plugins’. If you are running 10.6.8 or later:
When you have installed the latest version of Flash, relaunch Safari and test.
If you're getting a 'blocked plug-in' error, then in System Preferences… ▹ Flash Player▹ Advanced