The Masai were noted for their disdain for firearms. One widely-quoted report states that after massacre-ing an entire caravan of arab traders/slavers, the Moran laid several hundred arab bodies at attention beside a path with their muskets on their shoulders, and just walked away, didn't even deign to capture the guns.
If yours is an alternate Africa, then by all means use some fire-arm toting Maasai, but it might not be proper for an historical game.
Also, the Masai have a definite and distinct (long, storky) body type which Mark Copplestone captured astonishingly well in his sculpts. If you are talking about other figures which already carry muskets, then their body types will not match your Masai, and should look different enough that you might not want to mix them in. I certainly would not, but ymmv.