Unifi APs - Not passing guest VLAN through DLINK switches

Hey guys, this one has me stumped and I would appreciate some assistance.

We have a site set up with 15 UAP-AC-LITE APs and so far they are great and working fine for the internal wireless network.

However, I'm trying to get the guest network on a separate VLAN (I've designated VID 3 for it).

5 of the APs are going through DLINK DGS-3100 switches, and the rest are going through Ubnt Edgeswitches.

A USG is on the edge handling DHCP and internet access for the guest network, while the internal network is getting DHCP from an SBS server. Internal network is 10.10.20.1/24 and guest is 192.168.3.1/24 .

The APs connected to the Edgeswitches have the ports with the APs connected to them tagged as VLAN3 and the trunk port set on the uplinks - all clients connecting to those APs get an address and function fine.

Now, when I tag the AP connected ports with VLAN 3 on the dlink switches, and enable Vlan trunking on the upliink ports - all of the clients going through those APs fail to get addresses, or get bogus ones like 169.x.x.x or 10.x.x.x addresses.

I've even tried turning on DHCP relay on these DLINK switches pointed to the 192.168.3.1 DHCP server on the USG, but they can't seem to find their way there.

It's confusing to me because it seems like the DLINK switches are handling the VLAN traffic in an odd way compared to the EdgeSwitch connected devices.

Is there a setting somewhere I've missed? I don't have any experience dealing with managed Dlink switches, so i've tried all manner of combinations in the settings and it seems like nothing wants to work.

A side note: We had to add the Edgeswitches into the existing network because there weren't enough PoE ports available on the Dlink Switches, so they are all uplinked to these DGS-3100's (which means they are passing the vlan info when the tag does not originate on the switch).