I believe there's an mplayer - OS X version, & supposedly a frontend (like this one I found, w/o doing any research) http://mplayer-os-x.en.softonic.com/mac
Don't know anything about the frontend dev of that one.
On SMPlayer's SF d/l site, you have a UMPlayer version, but don't see one for Mac. The UMPlayer site http://www.umplayer.com/ says it's Mac compatible, but they may not be maintaining it anymore.
I'm just trying to find him something fairly easy to use - esp. for playing youtube / other flash vids. There's always VLC for Macs. I prefer SMP in Windows, over VLC, but sometimes Mac users can't be choosey w/ software, which is odd - they're VERY choosey about the OS.
Thanks.