[Al_The_Man]

I think you will find that scales will give you better accuracy everytime, due to the fact that they by pass the backlash etc, they are after all right at the final motion, they are not used often due to the high cost,They also need protection from coolant and chips etc.
There is no difference with interfacing them as they look like encoders to the control, as long as you have ones with square wave quadrature out, some have a sine wave out and should be avoided for this application. There are usually plenty of 3rd party servo amps on ebay etc and some of the makes to look for are A-M-C and Copley Controls both make very good amps and are easy to work with. You will probabally have less trouble with mix and matching DC servos. If you want brushless, look at brushless DC, as the motor resembles an AC servo but is easier to match up to 3rd party amps than sinusoidal AC types.
Al