Alright, I'll probably ruffle some feathers with this one, but I'll go ahead anyway. Feel free to take shots at me afterward as you please.
Personally, I see the practice as a cop out. I admit, I probably judge others too much for their RP, but to me its on the same level as the "child prodigy," the "empowered seductress," the "evil genius." They're the lowest common denominators in the RP sphere, and while they're interesting once or twice in your lifetime, they dull very quickly and detract from immersion. Admittedly, "silent loner" isn't very original either, but at least its less-seen.
HOWEVAR!!1!one
As for the legitimacy of the practice, purely in terms of plausibility, of course there shouldn't be a problem. Let alone in more tame MMOs, where it fits into the "dark underbelly" of the RP world. In EVE, the whole universe is a violent, dangerous, untamed, ugly place. We murder hundreds of millions of crewmen a day, for fun and profit. We produce and sell mind-melting drugs. We turn on one another through political espionage and corporate theft. We start small-scale wars based on race, religion, or sometimes just the nature of a wartime market.
Prostitution is very, very low on the list of things "wrong" with the universe. I may have my problems from an "RPer" perspective, but in terms of RL morality, its just another character. No one should catch ethical flak for the choice to RP a prostitute, because it's not them, its a character.
That being said, I love it and I'm never leaving. <3