Wiring the cap to the 3rd lug of the volume pot is fine. The pot and cap are connected in series, and it doesn't matter which comes first. The 3rd lug of the volume pot is a ground, and the tone network is connected to ground somewhere. It doesn't matter much which ground is used.
I often add a resitor to my volume pots to make the taper more like a linear pot, which gives a wider sweep as I roll down. Try it, you may like it.
Like chrom says, with the tone control wide open the cap is totally out of the circuit, so it won't be making the guitar darker. Even if he did use a .047uf cap (the standard value for a tele with 250k pots, btw), it just means that you get the same tone reduction with less rotation of the pot.