I wonder about this and am convinced that while it is possible, it will be a sideshow (like Manon Rheaume) more than a breakthrough.

There is no reason that any person throwing 70 MPH, especially an effective, moving 70 MPH, would not be able to get outs. We see it happen all the time when a position player comes in during mop-up duty of a blow-out. The bigger question is what happens when a professional sees it a second, or third time around the order. The Golden League, an independent minor league, had a female knuckle-baller who started, and she met with mediocre success. (http://sports.espn.go.com/espn/wire?id=5069754)

She was not bad, but neither was she able to consistently get outs.

Very, very long story short is that a professional team will use ANY advantage they can find. If they felt that a female pitcher was a better option than a current male pitcher they would include her on the roster. That being said, the very few opportunities that have presented so far have been more PT Barnum sideshow than Connie Mack brilliance.