You should *not* use vPC for L3 routed connections on the 7K. Just use regular routed links for L3 interfaces. It accomplishes the same result of active/active bandwidth with load sharing and fast convergence.
Like this:
On the 4K or 6K:
interface GigabitEthernet4/1
description Link to N7K1
no switchport
ip address 10.100.10.5 255.255.255.254
ip ospf network point-to-point
interface GigabitEthernet5/1
description Link to N7K2
no switchport
ip address 10.100.10.9 255.255.255.254
ip ospf network point-to-point
On N7K1:
int E1/1
description Link to 6K int 4/1
no switchport
ip address 10.100.10.6 255.255.255.254
ip ospf network point-to-point
ip router ospf area 1
On N7K2:
int E1/1
description Link to 6K int 5/1
no switchport
ip address 10.100.10.10 255.255.255.254
ip ospf network point-to-point
ip router ospf area 1
Make sense?
