You would need to create two different Virtual APs (VAPs). The VAP contains the VLAN or VLAN pool.
Assign VLAN x to the first VAP (where x is the VLAN where the DHCP helper points to one server) and VLAN y to the other (where y is the VLAN where the DHCP helper points to the other server).
You can reuse the same SSID, AAA, AP system and other profiles.