Hi Andrew,
I checked your configuration and exported Visitors WLAN to my cnMaestro account and tried. I'm able to get IP address for my clients. My setup is similar to yours, DHCP server is sitting in the upstream of the AP. Did a packet capture on the WLAN and eth 1 to verify that the DHCP discover packets are exiting the interface.
sharing the command below
E425-6EDEA1(config)# packet-capture wlan 1 udp
1 00:00:00.000000 18:db:f2:23:9f:32 > 01:00:5e:7f:ff:fa, IPv4, length 179: (tos 0x0, ttl 4, id 35287, offset 0, flags [none], proto UDP (17), length 165)
10.110.200.18.55355 > 239.255.255.250.1900: [udp sum ok] UDP, length 137
2 00:00:00.208533 e4:a7:a0:d4:31:c2 > ff:ff:ff:ff:ff:ff, 802.1Q, length 373: vlan 1, p 0, ethertype IPv4, (tos 0x0, ttl 128, id 40453, offset 0, flags [none], proto UDP (17), length 355)
0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] UDP, length 327
3 00:00:00.208577 e4:a7:a0:d4:31:c2 > ff:ff:ff:ff:ff:ff, IPv4, length 369: (tos 0x0, ttl 128, id 40453, offset 0, flags [none], proto UDP (17), length 355)
0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] UDP, length 327
4 00:00:00.211140 f8:0b:cb:98:a5:51 > e4:a7:a0:d4:31:c2, IPv4, length 377: (tos 0x0, ttl 255, id 63357, offset 0, flags [none], proto UDP (17), length 363)
10.110.200.1.67 > 10.110.200.48.68: [udp sum ok] UDP, length 335
5 00:00:00.248558 e4:a7:a0:d4:31:c2 > f8:0b:cb:98:a5:51, 802.1Q, length 87: vlan 1, p 0, ethertype IPv4, (tos 0x0, ttl 128, id 14648, offset 0, flags [none], proto UDP (17), length 69)
E425-6EDEA1(config)# packet-capture eth 1 udp
<SNIP>
39 00:00:03.538336 18:db:f2:23:9f:32 > ff:ff:ff:ff:ff:ff, IPv4, length 92: (tos 0x0, ttl 128, id 30357, offset 0, flags [none], proto UDP (17), length 78)
10.110.200.18.137 > 10.110.200.63.137: [udp sum ok] UDP, length 50
40 00:00:03.553833 18:db:f2:23:9f:32 > ff:ff:ff:ff:ff:ff, IPv4, length 92: (tos 0x0, ttl 128, id 30358, offset 0, flags [none], proto UDP (17), length 78)
10.110.200.18.137 > 10.110.200.63.137: [udp sum ok] UDP, length 50
41 00:00:03.925263 e4:a7:a0:d4:31:c2 > ff:ff:ff:ff:ff:ff, IPv4, length 369: (tos 0x0, ttl 128, id 40454, offset 0, flags [none], proto UDP (17), length 355)
0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] UDP, length 327
42 00:00:03.925437 e4:a7:a0:d4:31:c2 > 33:33:00:01:00:02, IPv6, length 166: (flowlabel 0x8d9b1, hlim 1, next-header UDP (17) payload length: 112) fe80::41f4:690:c919:6440.546 > ff02::1:2.547: [udp sum ok] UDP, length 104
43 00:00:03.928014 f8:0b:cb:98:a5:51 > e4:a7:a0:d4:31:c2, IPv4, length 377: (tos 0x0, ttl 255, id 63358, offset 0, flags [none], proto UDP (17), length 363)
10.110.200.1.67 > 10.110.200.48.68: [udp sum ok] UDP, length 335
44 00:00:03.938358 e4:a7:a0:d4:31:c2 > f8:0b:cb:98:a5:51, IPv4, length 79: (tos 0x0, ttl 128, id 14685, offset 0, flags [none], proto UDP (17), length 65)
10.110.200.48.50077 > 10.110.12.110.53: [udp sum ok] UDP, length 37
Regards
Anand