We have seen several situations where Windows DHCP servers don't function properly in a multi-VLAN environment. The failure mode most common to us is as follows:
Data VLAN served by Windows DHCP server. Phones in separate voice VLAN with a different DHCP server, typically the Adtran IAD. Phones act in trunk mode, passing data VLAN to a PC plugged in to the pass-through port on the phone.
PROBLEM: If the Windows server on the data VLAN is connected to a switch port that has the voice VLAN available, it will hand out data VLAN addresses to the phones, even if the voice VLAN isn't programmed on the Windows DHCP server at all. It will "jump" VLANs. The phones then fail to register or communicate with anything on the voice VLAN because they're on the wrong subnet.
The only fix is to connect Windows DHCP servers only to switch ports that are manually configured as access ports on the data VLAN only. Don't try multiple scopes on the same Windows server for devices on other VLANs.
I recommend ensuring that your Windows DHCP servers are on switch ports set to access mode serving only the VLAN where the Windows DHCP clients reside. Use the 7100 as the DHCP server for the voice VLAN.