That is a perfect application for the technique I described since it's a small dovetail and the material is brass. Just make a slotting tool with the angle of the dovetail align it with the bottom of the slot and work your way out each direction to form the angle, sort of like broaching. I would mill the cutter out of O1, harden it and stone the edges for a good finish or you could just grind it out a HSS bit if you have a way to hold it in the spindle (maybe a fly cutter). Don't forget to include a little clearance behind the cutting edge. You are correct, making a rotary dovetail cutter that small would be very difficult. The fun part is you can machine the whole thing without turning your mill on.
Tom