Sailors are also superstitious though and might not like the idea of one on ship. It is of course entirely up to the GM.
How badass is the Tiefling in question? Most of the inhabitants of the Shackles are at least neutral on the subject of open-sea piracy and tolerate just about anything tat isn't an immediate threat. If a tiefling has the interest in it, the Shackles might be one of the best places to hang out available to 'em.
As a GM: I ruled that generally being of devil/demon descent would come with a degree of prejudice and superstition. And I just figure a lot of superstitions of sailors can cause some... distrust.
I have a tiefling player, and she is a runaway pariah/Chelish slave.
I let the character's first feat be "pass for human." She hides her tail, and her small horns with a combination of hairstyle and cowl. Of course, after being stripped from chest up for whippin' a some characters have overcome her disguise DC.