I also contacted Pond5 support and asked whether I may leave my video files currently with Adobe if I sign up as an exclusive contributor. Ryans (Pond5) answer was loud and clear:
Thanks for writing in. No, you may not have the same videos on Adobe and Pond5 exclusive. If you are exclusive to Pond5, that means that the videos can only be offered on Pond5, or through Pond5 to our partners via the Global Partner Program (GPP).