The bees have access to several good patches of Gorse and i have watched them working it many times over the past couple of years, yes they do gather pollen but they also gather something else when burying there heads into the flowers, i have seen bees on many occasions going from flower to flower with no pollen loads while gathering something else and then flying off, if you are 100% certain that it does not produce nectar maybe it is propolis, either way i do not care as long as the bees are benefiting from this long flowering shrub..
Edited to add this link which is 50/50 whether it produces nectar or not..
https://easywildflowers.wordpress.com/2015/02/23/ulex-europaeus-the-common-gorse/