First of all, you can?t supply a machine with 240 volts, if it is rated for 208 volts. If the manufacturer has rated it to handle both voltage levels, then you can use the transformer that you named.
Secondly, regardless of whether a transformer is configured in such a way as to establish a separately derived system, you always have to worry about the sizes of the wires on both sides of the transformer.
Third, I don?t understand what you mean by saying the transformer will go ?in between that 480 volt circuit.? Do you mean that there is an existing circuit that has its own breaker (likely a 30 amp), a #10 wire, and some downstream load, and you intend to connect the primary side of your step-down transformer to that #10 wire, at some point ?in between? the existing breaker and the existing load? If that is what you mean, then yes you can do that, but only if (1) the wire you use as the primary to your transformer is no smaller than #10, and (2) the total load on the combined circuit (i.e., the new transformer and compressors combined with the circuit?s original load) does not exceed a total of 30 amps.