Adding vibrato to a bent note is a great way to keep the note sustaining as well as giving a more emotional quality to the music. When practicing this type of vibrato, be sure to reach the highest pitch intended for the bend before releasing the pressure slightly. Then increase the pressure again to return the note to its original bent pitch. Practice slowly at first and increase the speed gradually.
Here is a lick which uses vibrato on bent notes.
This one makes use of bent and unbent vibrato.