I got a message to the same effect a while back. The "pay" was shit so I didn't do it. But you can maintain anonymity as far as the public goes if you choose to do it. Just give them an alias to use. If they "out you" you can get a lot more $$ from them for it. Of course, then your life will be ruined, but...
If it is a legitimate publisher, publishing erotica, they will be more than aware of an author's desire to use a pen name. Some authors do, some authors don't.
Consider this: a person who writes erotica may have serious concerns about the public perception of them, and not just for modesty reasons. Many authors are concerned that readers will equate them with their stories, and harrass them. A person could write BDSM without being into BDSM, personally. But, just as with actors, some people have a hard time grasping that a person could create something without being personally aroused by it, or that it is anything more than fantasy.
As for the usage of a pen name when writing erotica, if you are truly concerned about the party requesting rights, then have it put into the contract that the publisher under no conditions is allowed to use your real name in association with the book (or in any way, other than paying you royalties or advance). Get a lawyer to look over the contract. Don't be afraid to ask questions.
Also remember that if the publisher is small, you have more negotiating power. That doesn't mean the publisher will give you everything you want, but will be more likely to try and work with you.
If you you can get past the legal concerns and the fear of exposure, then the main question should be if you really want the story published.