You can tell an AP what controller address to connect to, thru DHCP option 43 (sub-code 03 or 06 for ZD and SZ respectively),
or with 'set director ip a.b.c.d' for ZD managed, or 'set controller ip a.b.c.d' for SZ managed, where a.b.c.d is your controller IP,
assuming the AP has routing/network access to the controller.
Unleashed requires that all APs be on the same flat VLAN, so it would depend on if your VPN connected home looks like it's
on the same VLAN as the other Unleashed APs you're trying to connect to.