Leaving aside how you might feel about negotiating a first date with an outsourced proxy, it seems undesirable for the online dating sites to allow this (extremely profitable!) sideline to be captured by outside firms. One could imagine different tiers of service, through different front-ends of course, that tried to bridge the spectrum between the hands-on and hands-off approaches. Or is somebody already doing that? One could imagine that "specialty" dating sites (specific population, additional services, whatever) are cross-listing with "general" dating sites; there'd certainly be an advantage to both sides getting a larger pool to pick from.
There does seem to be some sort of need here... and yet, having the dating service company lie about who the message is really from does seem unethical. (Not that some of them haven't been accused of going even further and sending messages from purely fictional persons.)