If you are asking if multiple delegations, e.g. zone1.customer.com, zone2.customer.com, zone3.customer.com, can all point to a single SIP on the Isilon, the answer is yet.  A single SIP can support multiple subnets and IP pools.  It all gets resolved via the actual DNS name you assign to an IP pool.  Because each of the names must be unique, the Isilon can always figure out which IP pool to use when replying back to a DNS request.