My understanding is when the phone is on vibrate, everything vibrates. However, I'd recommend trying
VIP Ringtone to set up the contacts you want to get through. You can set the phone to vibrate and ring, and set the ringer to a silent tone for everyone but the people that ring.
Alternatively, you can use
V_vibrate to turn on/off your ringtones, and schedule it with
CT scheduler (there is a free and a paid version).