It depends where there tattoos are. If they are visible then I believe it is up to the employer to let them know what is expected. I can remember the one guy who worked as a technician on the road and had got a tattoo on his legs. He was banned from wearing shorts as it cheapened the image of the company. In some walks of life it is fine but honestly the business world wants professional people who look professional and a tattoo doesn't come across well if it is visible.
Would you honestly hire someone who worked with customers who had tattoos all over his hands and arms. If they are an artist or someone who works in an office environment then that would be different.
If someone was teaching children or someone who had an influence over children then I think it would be wrong to have tattoos in that environment.