wbrown I'll keep this fairly short as I'm almost done with my lunch break! This may simply be a case of using the products' capabilities appropriately. I don't want to get bogged down arguing for one product over another, but Infoblox is one of a number of DDI (DNS/DHCP/IPAM) solutions out there. If I read your comment correctly, your complaint is that you are using Infoblox only for DHCP, but you're not really using it for DNS or IPAM. You like Orion IPAM because of the scanning, and are frustrated that Orion and Infoblox don't integrate - but honestly, why would Infoblox integrate a competitor's product when they have an IPAM solution themselves? By the way, Infoblox NetMRI can do automated discovery / scanning for you I believe.
Subnets don't need to be DHCP assigned to justify being in IP Address Management solution either; whether you are assigning DMZ subnets or non-DHCP subnets, if you have an IPAM solution I believe there's benefit in using it. Start using it to drive your DNS as well, and the benefits are even greater.
I agree with you that scanning is very useful though - it really is helpful to have validation of what's out there compared to what's in the system.