Same VLAN and subnet? I think the iHost connects over local network so you could make this happen but by the time you know enough to create VLAN’s you likely know enough to put them one the same VLAN and subnet.
At least please make sure smart home devices are on the same subnet. eWeLink app may just check the online status on the cloud if it’s unreachable via LAN. You can check if there’s a smart icon right along with the device card on eWeLink app.