It is true that a software implementation needs a Dante clock leader elsewhere on the network.The H2 uses the Broadway that’s been discontinued and there’s no replacement for it. The H1 uses software based Dante which must slave to an external hardware based Dante device. In order to sync with the video, the source must have a hardware based Dante implementation. I know of no sources with HDMI outputs which also have a hardware based Dante implementation inside.
However for playback the clock drift between that and the video clock really isn't a concern and as I said previously the latency compensation will be done manually in a studio environment.
Having multiple clocks in the system is far more of a concern when recording where the differences in the rates between multiple devices can and do cause takes to be slightly different lengths on playback.