Config looks good... almost
If you have no problems with statically configured clients, it's just saying about you have problems with DHCP-RELAY or with DHCP-SERVER 
1. What do you see in the dhcp log of the server?
2. Do you ever see any errors on the server's log? I'm sure, it's something easy and before the eyes.
3. As Steve said earlier: You should turn on traceoption for helper on QFX for much more detailed info gathering.
If ae0.0 just a trunk, you can made "delete forwarding-options dhcp-relay group relay-svrs interface ae0.0" on the QFX