I know especially when porn stars first started escorting some would say it would be videotape, provide a model release, etc-  but I don't think the video taping really gets around anything- unless you have a legit company, contracts, set, etc- its not really meant to be a movie which would be pretty easy to prove- that being said, if you do your research and meet well review provider/ porn star what are the chances of getting caught?  most of the busts reported are LE going after craiglists and backpage ads, never heard of any one getting caught with a pornstar though guess there is a first time for everything

Shooting porn is actually only "legal" in California based on Supreme court ruling from decades ago.  Even in California permits are required the same as they are for any movie shoot.

It depends upon the law in the state you are filming.  Do you really think all these reality porn sites get a permit everytime they shoot? If you don't say anything stupid and you have a good lawyer it would be difficult to be convicted.

IIRC, this was tested once in court and the answer was "no".  However, since I don't believe that case made it to the federal level, it might only be relevant in that state.  I'm not sure which state it was - I think Arizona.  Maybe a lawyer could look it up?