Not mandatory. The TS can transmit a value which is not necessarily used by the roll off filter in the DVB-S2 encoder.
At least this is the case in the MiniTioune software in combination with F5OEO firmware.
With the hardare solution used in DOHA, you can assume that the rolloff value supplied in the TS is also used in the DVB-S2 encoder.
73 de Robert