No, Will, the effect of the crossover on impedance has to be taken into account. At say 50Hz the woofer impedance would be about 4ohms, but the crossover would have the tweeter impedance much higher at that point so as to roll off its response. If for example the tweeter impedance that the amp "saw" at that point was 100ohms rather than its normal 4ohms (because of the crossover) the net parallel impedance would be 1/R=1/4+1/100 or 1/R=26/100 or 3.85ohms. The parallel connection doesn't result in a halving of impedance since the impedances seen by the amp aren't the nominal equal ones of the drivers.
