Sure, you can add USB devices to HA VM in ESXi Server. I use this configuration for few years by now, initially with ESXi 6U2, since few months with ESXi 8. Hre is configuration of my VM:
As you can see I have 2 USB devices, Conbee II and Aeotec Zwave Gen 5 sticks connected to HA. Working flawlesly. It is done on VM configuration level, as ESXi server does see devices conected to hosts USB controller. It is not passthrough, as required for PCI devices.
Regarding your setup, as I understand you run Deconz on separate machine, so you can migrate to Deconz add-on (as I have it configured) and reconnect stilc to Deconz running inside HA VM. I have no experience with Silex stick, but I’d assume that it could be connected exactly same way. Just make sure, that inside your HA VM you also configured USB controller (you can see on screenshot, but I think it is added by default to HA OVA file already).