Yes, they all did...went from 70+ to -3 to -15 with Ragnar after our last war, and 100 devoted to me thanks to high honour.
There is definitely a sweet spot for converting lords.
I also convinced a cunning Rhodok lord to join my empire, bringing Ergellon, Grunwalder and Weyyah castle into the fold. Then I indicted him for treason, as it's only a matter of time before he betrays me too, (learned that lesson well!) and divvied out his former castles to my loyal devotees.
It's a tad powerful being so 'good'...