I'm not a Minmatar RP'er so take my input with a grain - or ton, of crude, grain-sized transparent crystals.
Building on what others have said here and my own previous comment I really see no reason why Anslo could not have earned a tattoo of some kind. Matari are as diverse as anyone in the Federation so, while some Matari (like the ones he frequented, for instance) may not take it too seriously that a non-Matari earned a mark of serious respect among them for some great deed or other, other Matari will take offence with him having the tattoo AT ALL, simply because he's not a Matari by blood. There is likely always going to be people like that among humans, I see no reason why this is not so thousands of years into the future.
However, some Matari disagreeing in principle is irrelevant to Anslo's earning of this mark. If a group of Matari of some stripe or another considered Anslo valuable enough to have earned it, then that's that. In fact saying no to receive this mark might be taken as a sign of disrespect in itself (even if I really hate the "disrespecting my gift by not taking it" trope myself) and his defense in the face of critique will always be "I earned this from your kin, back the fuck off or take it up with them."
End of the line is, if Anslo earned it legitimately, why should he bend over backwards to the opinion of some intolerant Matari? Why is the words of a Matari automatically more valuable than his own, especially when the deed speaks for itself?