I'm going to be using it with Sky fibre. Currently I have a Asus AC68U connected to a HG612 and use option 61, I don't have VLAN IDs set anywhere but maybe they are default as 101 on the HG612?
There are actually two VLANs configured in the HG612, by default. The HG612 is the end-point for both VLANs, they do not extend over the Ethernet link to the user's equipment. They are tagged 101 and 301, respectively, with the 101 VLAN carrying the service data whilst the 301 VLAN was used for service performance monitoring, administration and firmware upgrading processes. (The infamous BTAgent made use of that VLAN tagged 301.)
When configuring the ZyXEL device, just ensure that you define a VLAN tagged 101 and all will be well.