I'm on steam beta 2.5.6 also. I had the same problem with loading stopping at 10%. Then I did specify the steam dcs world directory on the config page and ticked the OB checkbox.
Now on loading vaicom finds first the steam install, places all the files there and in saved games/dcs, then proceeds to the specified OB path, which is the same, and overwrites all the file with the correct OB ones.
Then creates a saved games/dcs.openbeta directory and places the same file as in saved games/dcs previously.
It works for me now like that.