[mcnallym]

Hide NAT if you have ISP Redundancy needs to be set to Hide Behind Gateway so that it hides behind the gateway interface that it leaves from.

There is also an excellent article in Check Point knowledgebase that explains exactly what needs to be done to create working Static NAT and Hide NAT with ISP Redundancy as it is not the same as in normal mode where you need to create dynamic objects and then define them on the local boxes themselves to get it to work.