all the random number streams are handled in a centralized way in CDF2SIM by a single random number (RN) manager

all the random number streams are named

to initialize Herwig RN stream from within CDF2SIM:

AC++> root TRn::Instance()->Init("Herwig",seed1,seed2,seed3)

seed1 : (INTEGER) Seed from which the sequence was started.
seed2 : (INTEGER) Number (mod 10^9 ) of random number generated so far.
seed3 : (INTEGER) Billions ( 10^9 ) of random numbers generated so far.

so normally it looks like this:

AC++> root TRn::Instance()->Init("Herwig",1,0,0)

The seeds are the ones taken by the underlying RN generator (CERN V113) -
see 
                 http://wwwinfo.cern.ch/asdoc/shortwrupsdir/v113/top.html

for more details.