Sunn hemp (Crotalaria juncea) requires pollination to set seed. The large pea flowers are naturally pollinated by large solitary bees. A Florida professor has a 2010 research effort to evaluate Carpenter bees as a pollinator for seed production.
Most large pea flowers have a triggering mechanism to restrict pollinators to the co-evolved species. The flowers only opens to expose the stigma for pollination when the correct weight of the insect depresses the lower petals. In general the reward of these flowers is the pollen, and not nectar. The larger flowers (such as in Sunn Hemp) usually require a bee heavier than a honey bee to trigger the opening. Honey bees may visit the flowers (and obtain pollen) but are not effective pollinators.
Scotch Broom (Cystitus scoparius), a shrubby, weedy pea relative and common invasive species on the west coast has a tripping mechanism that dusts honey bees with pollen. It is quite explosive, and bees visiting the flowers get irritated and ready to sting from the abuse heaped on them by the exploding flowers. Bee away from the hive don't usually sting, but those visiting a broom plant will at the drop of a hat. The abuse doesn't stop them from visiting and tripping the flowers obsessively however, must be pretty good pollen.