I don't have any direct experience with these, but I still have an opinion:  Any spoiler system can exhibit asymmetric deployment, so the plane should be (easily) controllable regardless of the spoiler symmetry.  A spoiler longer in span and less in height might be more of a challenge, but I would think not.  If the spoiler is hinged at the front, hydraulically powered and reasonable friction free there is a good chance that the deployment will be equal, even at partial deployment - but not necessarily.  How are the spoilers retracted?  Springs?  Double-acting cylinder?  I wouldn't count on aerodynamic forces to return it completely flush with the wing.  Is there a spoiler only on the top surface?  If so, the roll moment will probably be significant in case of asymmetric deployment.  And the comment before about the advisability of tapping into the gear hydraulic system is something to consider.  Go to a manually-pumped hydraulic system with a dedicated reservoir?