Do you have a Layer 3 device to connect / route between the VLANs?
Even if your DHCP server is on the AP, DHCP service are only available on the native VLAN. To get the DHCP requests/replys to other VLANs, you need a layer three device (router or L3 switch) to move the traffic from the native VLAN to the other VLANs.
Which VLAN is your DHCP server connected to? Is it on the native VLAN?
Do you have IP-HELPER configured on the AP-side of the switches virtual interface? DHCP starts the transaction with a broadcast from the client, routed interfaces block broadcasts by default, so you'd use IP-HELPER (only on the client-side of the interface) to forward those requests to your DHCP server.
The RADIUS requests work because they are unicast, and can be normally routed.
And, while you do not explicitely say so, I'm assuming that you have L3 mode enabled on your 3750, and each VLAN presents a routed interface.
Otherwise, just having the various VLANs hosted through a device doesn't mean they'll talk to each other. They are logically separate broadcast domains and require something acting as a router to move traffic from one VLAN to the other.
I have re-configured from scratch again, and i encountered DHCP problem. My test results shows that when i am using static IP, everything works well (including from different VLANs w different SSID). When i set "Auto DHCP",
via > AP > 3750 - fail,
I believe its the IP-HELPER you mentioned earlier.