I would say no, because:
1. Although a shadow creature is composed of shadow, it is no longer truly a real shadow itself.
2. I do not believe that the rules intend for this little loophole - to be able to use this ability in otherwise brightly lit area by using your creature.
3. It is generally not too difficult to find shadows... just look around; they are everywhere.
in our campaign, the shadowdancer uses the goliath's shadow for all his abilities lol. But a shadow creature is no longer a shadow, its a creature. so no, id rule you cant use a shadow creature as a valid shadow for shadowjump(or HiPS)