It certainly is reasonable to use a tattoo to camouflage a scar, but I would suggest waiting to till the scar is done healing before getting the tattoo.  We like that scars shrink - but if you tattoo over a wide immature scar and then it shrinks, it will compress the ink along the scar line and this maybe very noticeable.  Everyone heals at a different rate, but when the scar is flat and white, you know you are done.  In the meantime, it is worthwhile using scar creams to help accelerate the healing process.