Not sure. I believe the tools can be called from Arc Python, but I'd like to see some Arc Hydro specific code so I can make an easier transition from Model Builder to Arc Python.
Just did a web search using Archydro and Python and there are a number of threads, including one with you in it, It appears that things are largely a shell around the spatial analyst tools. In any event, you might want to do a search there, if there is nothing in the Archydro place ...
Basically you need to add "import ArcHydroTools" a the beginning of your script.
Then you can access the tools using ArcHydroTools.DrainageLineProcessing()
You can test it in the Python window in ArcMap.
>>> import ArcHydroTools
Esri Water Resources Team