Sumacs have many great attributes, being
native plants, good for
bees and birds, great for erosion control, tolerant of poor soils and prolonged drought, and no real pests.
Their pretty look and spreading habits may be too bold for some.
I have never heard of them as being nitrogen fixers.
Most folks do not understand nitrogen fixers, it is not planting them though to be a nitrogen fixers them are trimmed so that their trimming go back into the soil ...