This is a good question and i wish to know its answer as i have found contrasting papers with regard to this parasitic and legume nodulation. I don't know if really contrast between legumes occur or people publish to be different...
is just an assumption, but it is known that B. elkanii, for example, produces IAA that is related with nodulation capacity, so in the case of faba bean, maybe the production of this auxin favors the appearance of this parasitic plant (Orobanche), once the orobanche is a sink of auxin. For more informations look of papers attached. So, others rhizobia maybe produces IAA during nodulation.