Hi,
Just an update: After some additional analysis we have found out that network connectivity problems are related to switch uplinks. We have created standard switch and connected management uplink + one of the other uplink (may it be iscsi net - without any storage device connected, only the physical switch; or the secondary LAN network). As soon as some other uplink is connected, the hosts loses its connection. The same happens with dvSwitch.
That said we have created two dvSwitches - one of management traffic and the another one for all other traffic. And woila - now the problems has gone, host doesn't lose connection any more, reboot is OK, hw status is OK.