Yes, don't worry. I've overclocked all my components for years and I've never had a part fail. Tons of people overclock the CPU it's no problem at all. Heat is the real killer of components, not "how hard" they are working.
There's no reason worrying about your video card. It's rendering the game. If it lowered the clock speed, your game performance would suffer. It is not designed to do this. They are literally designed to play games for extended periods of time. People that do bitcoin mining literally have their GPU's running at 100% for 12 hours+ at a time.