I don't know from any personal experience, but I reviewed some patents covering these devices and read some data sheets for products from different manufacturers. I believe that the terminator contains a resistor, and possibly a resistor in series with a diode. Each terminator would contain a different resistance and the possible range of resistor values is likely somewhere between 1K and 8K ohms. I note that the terminator cannot be anything fancy or the cost of the product would be higher than it is. The patent that I found covering a LAN cable mapper clearly indicates use of a resistor for identification. All the mappers place a maximum value of 100 or 200 ohms on the cable being measured, which leaves plenty of room to identify resistor values more than a few hundred ohms apart.
As far as i can see, these cable mappers (the kind that cost between $30 and $200) do not identify cable numbers using tones. In each case that I found, the tone function is an additional single output used for locating one cable at a time, not for indentifying multiple runs at one time.