I can see that proxy arp is enabled in the configuration above so that part should be good. And the policy seems to match the forwarding.
Since there are no hits on the policy from your connection attempts, try moving the vip policy to the top of your untrust to trust policy list.
If that does not work. Run debug flow basic on a connection attempt and let's see what the processing path is.
https://kb.juniper.net/InfoCenter/index?page=content&id=KB12208