This is a tricky subject. I think part of the problem with the failure of the regulatory regime was that those in charge didn't really know what was going on. Financials/trades got very complex - and many high level regulatory people admittedly didn't understand derivatives, CDS, and other complicated assets that blew the bubble.
So what do you do if you're Obama? Do you try to find a scrupulous person who is operating in this market and who understands what is going on at the edge of the envelope - but who runs the risk of being, as you say, a fox in the henhouse - or do you install someone from the outside who may be "out of the game" sufficiently as to limit effectiveness?
I don't think it is patently objectionable that the new SEC chief comes from industry. Hopefully, they picked a sharp, scrupulous person who won't be afraid to challenge the industry when necessary.