There should be a check when creating a route that the outgoing interface actually exist.

It's possible to create it regardless.

example of such as route

> PUT /restconf/config/hc2vpp-ietf-routing:routing/routing-instance/vpp-routing-instance/routing-protocols/routing-protocol/static-routing-2/static-routes/hc2vpp-ietf-ipv4-unicast-routing:ipv4/route/3232266243

Formatted JSON Data
{  
   "hc2vpp-ietf-ipv4-unicast-routing:route":[  
      {  
         "destination-prefix":"192.168.120.3/32",
         "id":3232266243,
         "next-hop":"192.168.120.3",
         "outgoing-interface":"neutron_port_db8b395b-7045-496f-ae98-61ccd5d29a37"
      }
   ]
}