Yes and no. No, if it is one wire or two wires in parallel (the feed line) doesn't mater. But yes, the resistive losses in that counterpoise will generally be much lower than the alternative, the soil nearest to the fed end / feed line / rig. Try to look at how the antenna functions in free space, without any feed line (that is not part of the antenna as in the case of the Zepp), and with an infinitely small transmitter. If you remove the matching section from the Zepp, and the physical size of the transformer and rig, where is the current in the feed point (even if it is small) going to go?