I dig up this thread just to thank you, that tip saved me from a lot of problem.
I wasn't aware of
source-address-giaddr
And I had to configure a special NAT rule on the router between my ex3300 and the DHCP server which claim a source ip from the served subnet. I tested from the subnet matching the nat adress on the router and it worked, but when I tried today from the second subnet it didn't
The above command set on both vlans did solve my problem as I added a rule to not nat dhcp/dns request comming from these two subnets ips.
You saved my day !