Quick Question about Guest Network and NAT Loopback.

[SaBl]

Might be a stupid question, but I have a N66U. Most of my devices are on my regular network however I have family members' phones, tablets, and any guests' devices connect to a guest network. I have access to the intranet disabled for the guest network. I recently got a NAS and will be setting up family members to access it to backup files etc. If I connect my phone to the guest network I can access my NAS using the DDNS WAN address just fine. I'm assuming the NAT loopback is working correctly and reroutes the packets to the NAS despite the fact that intranet access is disabled for guest network? Would this setup be OK? I'd like to keep all those phone and tablets on the guest network.