May I connect two z-wave dongles with different freq

E.g. European 868.4Mhz and Israeli 916Mhz using USB nub connected to HE, and then manage elements with those freq?

The hub only supports one at a time. You could get a second HE hub though and add the Zwave frequency devices to their respective hubs. You would then use one of the hub connect drivers to join the two.