Well, most of Bhaalspawns from BG1 and BG2 had these dark urges born of their father's inheritance. Some gave in to these urges and most of the time it gave them a power boost.
But others, like CHARNAME, had strong enough willpower (albeit often low wisdom since it was a known dump stat) so they managed to resist this urge and were even able to change the dark power into good power. (Your Bhaal powers are dark combat spells if you're evil, or healing and buffing divine spells if you're good.)
If Dark Urge follows a similar example, then even trying to resist an increasingly strong urge could lead to interesting rewards and an interesting endings.
