IMO, the answer to the need for some backlash is, yes. A small amount of backlash is needed to allow for the oil film that needs to exist between the gears.
The article mentions the increase in the distance between the gear centers because of thermal expansion.
A close estimate of the thermal expansion between the gear centers depends on the size of the gears and the temperature rise from room temperature where the gears were adjusted.
I don't know what the size of the gear teeth are on the RE cams but they look like 20 pitch.
If this is true, the 20 tooth drive pinion on the crankshaft would have a pitch diameter of 1.000 inches. The 40 tooth cam gears would have a pitch diameter of 2.000 inches.
That makes the theoretical mounting distance between the gears (1.000/2) + (2.000/2) = .500 + 1.000 = 1.500 inches.
The difference in the rate of thermal expansion between aluminum and steel is approximately 6 X 10^-6 inch per inch per degree F.
At a crankcase operating temperature of 250 degrees F that would be equal to a temperature rise of 250-70 = 180 degrees.
180 X (6.0 X 10^-6) X 1.500 = .0016 inches so the distance between the crankshaft and the exhaust cam center will increase by that value. This conceivably could create enough backlash in the gear mesh to allow for a lubricating film
but what happens at 40 degrees F? Or (for those brave riders who go forth in the wintertime) 28 degrees F? (Been there, done that).
At these sub room temperatures, if the gear system was adjusted to zero backlash at room temperature, it would be running with a interference between the gear teeth at the temperatures below 70 degrees.
A interference between running gear teeth makes heat and wears the surface. Heat expands the gear leading to a increase in interference. Definitely bad.
As I mentioned earlier, IMO it is better to have a slight amount of backlash between the gears at room temperature. That backlash allows for a constant oil film to lubricate and cool the gear mesh and to allow for cold conditions during the winter.
My apologies to those who don't like math. Just ignore the number stuff and read the rest.