So, this company is going to do a "collected works" of everything you wrote on the net and SELL THAT INFORMATION TO A PROSPECTIVE EMPLOYER. Seems to me that's a commercial use of someone else's property (your words with copyrights), and you can't ordinarily do that without a release from the owner.But it could become universal that you are required to "voluntarily" sign such a release with your job application. They do that with other similar things, and get away with it because the courts would just say "Well, if you don't want to disclose it, don't sign, and get a job somewhere else." The courts don't specify where the "somewhere else" is.
In the past, some employers have required the applicant to list what blogs, social sites, etc that he may post on, and what his IDs were.
ACLU filed suit against the Maryland Corrections Department over their policy of having applicants supply their facebook ID and password so the interviewer could see everything they posted.
Yes, you can choose to omit your FR user ID, but keep in mind that lying on an application can be grounds for termination.