Is there a difference in heat produced on a conductor between AC and DC at the same amperage and voltage?
Yes... assuming for AC you mean 480V RMS, not peak-to-peak.

The power (in watts) should be:

480V * 50A = 24kW

However if you are measuring 480V AC peak-to-peak, the RMS voltage will be ~340V, in which case the power would be less:

340V * 50A = 17kW

AC voltage and current is continuously variable in a sine wave. Power is calculated using RMS so that it can be compared to DC in a useful way.