Tattoos on Holocaust survivors should be a badge of pride. I remember when I was young, the cook in my yeshiva had a number tattooed on his arm. When I was old enough to understand what it meant, I had a tremendous amount of respect for him. To go through that hell, and come out as a frum Jew, is amazing. I’m sure when these people get to their din v’cheshbon after 120, the tattoo (together with the yellow stars many had to wear) acts as a shield against the prosecutors in the beis din.
The Satmar Rebbe z”l, said that if you see someone with a tattoo from the camps, you should ask for a bracha from the person.To my knowledge, he didn’t say the person had to be frum, just that they have a tattoo.