Yeah... I don't think there should be any problem. Especially after three weeks, the tattoo should be pretty much healed. You have to wait after getting a tattoo to donate blood, but that's because of the risk of contracting an infection (HIV, hepatitis) from the tattoo and then spreading it via blood donation. But there shouldn't be any risk with having surgery, as long as the tattoo is healed. I guess if the tattoo wasn't healed, there might be some sort of risk of infection or problems healing because of the stress of surgery. You can always inform your doctor and make sure it's not a problem.