Medicals
For the physical examination,no one will undress you. The doctor which will be the same sex as your gender will ask you to take off your clothes for physical examination. You get to keep your panty and bra on (undies for the guys) so no worries!
The tattoo in the OK area should be fine. I had a batchmate who had one in her right shoulder. I don't know about the whole declaring it or not though. They do handle it in different ways somehow.