The urethra is the internal tube that allows urine (and semen in males) to exit the body. You really can't see it except for the opening the external urinary meatus. The urethra is red in color but many different diseases (including herpes) can cause redness.
Yes, herpes can cause a red urethra. Other symptoms include sensitivity, blisters and burning during urination. You should consult your doctor if you are experiencing these symptoms.
A reddening of the urethra is not typically a symptom of STDs including herpes, and is most likely a skin irritation. Consult your doctor if it doesn't clear up.
Yes it can cause inflammation and burning on any part of the genitals, including the urethra. The symptoms should subside in a week. If not, I would see a doctor.