My name is ***** ***** I would be more than happy to answer your legal question today. Your question, as most legal questions, are not as clear cut and thus, cannot be answered with a simple "yes" or "no". As you are aware, prostitution is illegal in Clark County (where Las Vegas is located).
Prostitution in Las Vegas includes any "touching of sexual organs" done in exchange for money. As you can assume, many massage parlors operate under a "guise" of being a legitimate massage business, but in fact, host prostitution.
You're safer bet would be to look to see if the parlor is licensed under the state. I say this because, when police see an unlicensed parlor in Nevada, and especially Las Vegas, they will assume it is a "front" for prostitution. If they raid or pay a visit to the parlor at a time you are there, you could be arrested and charged with Solicitation.
So, to answer your question. Are nude sensual massages legal in Las Vegas? The answer is yes, so long as there is no genital touching and/or sexual activity (which encompasses the typical sexual acts that often come to mind when you think of prostitution).
I hope I've been able to answer your question. If you have any follow ups, please let me know and I will be happy to answer them. If not, please remember to click "accept" and live positive feedback so I may receive credit for my response. Thank you!