But I currently try to connect them via OSC (OSC4Bitwig on the BWS-side) which I have partly working (Usine starts to play when I start BWS and song tempo is sent too).
It also seems to be possible to sync HH to BWS with Midi Beat Clock but so far that didn't work in my tests, still investigating what I do wrong.
My audio interface has no problem running both Bitwig and Usine on Asio at the same time it seems (Scarlett 18i20 with latest beta drivers) so I can send audio through that directly.
But I'm not into perfectly synced music so your mileage may vary
Rewire for Usine is also planned, in that case it would be possible to use Rewire-VST in BWS with it.
Cheers,
Tom