Is a raised floor viable and safe in a basement bathroom?
Why does he need to move the plumbing in the first place? My guess is that its simply because the drain in the concrete is in the incorrect place? I finish basements professionally for a living. Very rarely do you have the luxury of the base plumbing being in the exact right location. In almost every job that I do we move the tub/shower drain.  If you are using an experienced, professional plumber, this is a no brainer. Unless, of course their is a grade issue where he can't get the proper fall. However, if there is an existing drain under the concrete, this is a very unlikely situation. If we are moving plumbing less than 3' we use a jack hammer. if it's more than that, we saw cut. The previous reply is correct about the dust and mess of concrete saws... and it's more expensive (typically). If you are tiling the floor, just ensure that your concrete patch is very level (or just below the concrete grade) and then level quick the patch after the concrete is done. The fact that a jackhammer makes a 'jagged edge' hole is ok if you are installing flooring over it, as long as the patch is level.

For time and costs... my plumber charges $75 per hr for jackhammering (usually doesn't take more than an hour). Labor and time to rebase the drain into the correct location - $200-$350. Concrete patch - Less than $100.

To me its a no brainer... do it the right way, move it and repair the concrete. If your contractor has an issue with that, he may not be a contractor you want to finish this project for you.