Hi Rob,
With the 6525 you are ging to need an external source to drive the servo. I see the current limitation is 500 mA for the relay output and I believe most servos use more current than that, so I would not recommend it. You might try using a second external power supply and use the 6525 to trigger an external transistor to allow current to your servo.
Let me know how else I can help with this.
Regards,
Nathan B
Applications Engineer
National Instruments