After scanning the online documentation for the NW5.1 DHCP server, it
doesn't appear as though DHCP option 77 (user class) is supported. Did I
miss something? Is there a patch, or configuration change, that will
provide support?

Is it supported in 6.5?

If it is supported in 5.1 or 6.5, can I set different scope options based on
class? IOW, if the user class is "foo" set the DNS to and setup
a static route (option 33) to, but for the default (aka blank)
user class set DNS to with no static routes?