Hi Zoran,
It depends on how smart the servo actually is.
The Unitronics Vision series are great PLCs, but the scan time is not fast enough to serve as a true motion controller. So, the servo has to be able to take care of reaching the target position on it's own.
If you are doing point-to-point movement, triggered by input, then the Uni will do fine.
If the servo supports modbus, then you can change velocity and target position, and read current position over the serial link. I've done this with Automation Direct's SureServo line without alot of trouble.
If you want alot of sophisticated servo functions, or want the drive to serve as an amplifier only, better get a motion controller to go with the Uni. Trio makes some nice simple models.
TM