If the braces are on the front of your teeth, your lips should be covering your teeth while giving head or kissing. So the braces shouldn't be scratching anything. And if your lips aren't covering your teeth while giving head or kissing, then you're doing it wrong and you're probably already hurting whoever you're blowing.
You might not be able to kiss as vigorously because the friction on the inside of your lips might be too much. But that's more about pain for you than for your partner -- and you should let your partner know that they shouldn't be kissing too firmly either. You have a right to make them adapt their style to avoid pain for you.