The phenomenon is real, but the first explanation is wrong. For an account of what happens, help yourself to a very good answer at the Seasoned Advice StackExchange.
Basically, there are various droplets in scotch that take up or release molecules relevant to taste and odour, depending on the alcohol concentration in the surrounding liquid. This is a physical process, there are no chemical reactions involved.
Now things get messy.
So cooling and adding water can have the effect of both masking certain flavors by forcing them out of solution, and enhancing others by promoting their release back into solution.
This contradicts the second explanation, which relies on warming to improve the experience. But it also contradicts received wisdom, aka snifters! Can it be that this is one these popular, plausible explanations which turn out to be vaporware? (Pardon the pun)
Let's estimate the temperature increase from adding water.
The heat of solution for alcohol in water in the range of interest is about 200 cal/mol.
The specific heat of scotch is roughly 0.8 cal/g/K, if we take it to be the average of ethanol and water.
One drop is about 50 mL, or 0.05 cm^3.
The molar volume of water is about 18 cm^3/mol.
Five drops, as suggested in the question, are 0.25 cm^3, which amounts to ~0.014 mol. Multiply by heat of solution to get the amount of heat contributed by the added water: 2.8 cal. (That we add water, and not alcohol, as in the heat of solution diagram, should make no difference, the moles are important here.) Assuming our scotch glass holds 60 cm^3 (~2 fluid ounces, as recommended by Scotch Doc), its specific heat would be 48 cal/K. Divide heat added by specific heat, and you get a temperature increase of ~0.058 K, or ~0.1 F. I'm pretty certain that that is not nearly enough to noticeably increase evaporation, especially not compared to the contribution of swirling. But five drops is the straw method from Scotch Noob. The Doc recommends half a teaspoon (2.5 cm^3), which is ten times as much. I can't tell whether 0.58 K should make a difference.
It is claimed that snifters function in part by heating the juice, but how much the warming contributes to releasing aroma is anybody's guess. The experimental data acquired with beer only show that if the warming is important, a few degrees should suffice.
Answers that leave me confused: Go home science, you're drunk. :P
