What's this mark on my chainstay?
I have a Cannondale Supersix Evo and I've had issues with tires rubbing in that exact spot.  The frame will accommodate a 25mm tire, but the clearance is very tight, so you really have to pay attention to keeping the wheel trued up.  I've also found that the stock wheelset (Mavix Aksiums) flexed enough when I'm cornering hard to cause a little rubbing even when the wheel is near-perfectly true.  For a little while, I put some protective tape on the chainstays (I used ISC Racers Tape), but I eventually just switched back to 23mm tires. I like the ride quality of the wider tires, but replacing the protective tape periodically got to be a bit of a hassle.

To answer whether or not it's safe to ride, it LOOKS like it's just through the paint. If that's the case, cover it with some protective tape to prevent it from rubbing into the carbon, and you should be good to go.