Isilon really only has 1 default gateway.  The one with the highest priority is the default gateway.  The other default gateways will only be used if the primary default gateway is not available.  What this means is that only 1 subnet really gets a default gateway.  In the instance of a DMZ where connections could coming from a ton of different networks the best is to have the default gateway be in the DMZ and then have static routes defined for all the routes into the prod network.  And in general it would be a best practice to only configure a single default gateway for the entire cluster to avoid confusion.
We have two different subnets:  Prod:  10.0.2.x , gateway 10.0.2.254  DMZ:  10.10.54.x, gateway 10.10.54.254  Currently we have both gateways defined however or DMZ clients are having connection issues.
How does Isilon handle multiple default gateways?