Can you share the error you are getting. I am able to configure the same on cluster ruiing 12.1X46-D25.7
{primary:node0}
root> show configuration | display set | match reth2
set interfaces reth2 vlan-tagging
set interfaces reth2 redundant-ether-options redundancy-group 1
set interfaces reth2 unit 1150 vlan-id 1150
set interfaces reth2 unit 1150 family inet unnumbered-address lo0.1
set interfaces reth2 unit 1151 vlan-id 1151
set interfaces reth2 unit 1151 family inet unnumbered-address lo0.1
set routing-options static route 10.0.0.2/32 qualified-next-hop reth2.1150
set routing-options static route 10.0.0.3/32 qualified-next-hop reth2.1151
set security nat proxy-arp interface reth2.1150 address 10.0.0.0/24
set security nat proxy-arp interface reth2.1151 address 10.0.0.0/24
{primary:node0}
root>