I'm pretty close to a sp who works at one of the mentioned agencies, and we've talked about the whole thing of her working in the biz and for her agency. She is genuinely happy to be working for who she is. Technically the agency owners are her pimps, however the negative connotation associated with that title doesn't exist in their professional relationship.
She has related how one of the owners personally drives her to appointments when it's a new client. There seems to be an honest mutual feeling of care between that agency's owners and the sps that work for them. This isn't to say that there aren't bad things about working for them. On one hand the agency somehow made this girl's less dependable nature better, and on the corollary, the agency owners also made her work significantly more than she desired at times. One night that comes to mind is where she wanted to hang out with me after she got off work, and by the time she got to my place she was so tired that we just talked for a bit, and she simply passed out from exhaustion in bed.
Like everything in life, the concept of an agency is full of good and bad. But it does seem like there's more good than bad in the reputable agencies. Pimps in the official terminology seems correct, but certainly these agency owners don't deserve the stereotypes of being money extorting thugs as the word implies.