I'd say it's about equivalent to calling someone a 'hooker' or similar, so definitely not ideal. I suppose just how offensive would depend on the context though. As part of the dialogue in a novel it would be different from in an academic textbook!
I suppose the question then is whether the impression the word gives is what the author was aiming for. If he/she said the equivalent of 'slut' or 'gigolo' in the other language, then it's a fair translation even if the word is offensive, because that's what the author was expressing.
But if they said 'male escort' or similar, then the meaning has been changed by the translation.
But if what you're saying is 'this version, in this translation, uses offensive terms' then I'm with you.