Servo motor signal voltage vs "working" voltage
Most hobby servos will work with a 5V PWM signal (and I know from experience the Hitec HS-311 and a few others will even work with a 3.3V signal), but only specifications will give certainty.
Try googling the servo brand and type, and see if specs can be found. If you can't find specs, consider buying an other servo that does come with specs, or take the gamble.