There are two types of PS/2 to USB adapters, passive and active. Passive is what most adapters are, just a physical rewire dongle, and rely on the encoder board to be know when to send USB signals instead of PS/2. Active take the PS/2 signal, translate it to USB so can be used on old encoders that can't send USB signals, are more expensive, and generally suck for gaming due to designed just for typing documents (latency, low max simutanious key press, unable to hold down keys for long, ect).
Assuming the hotrod encoder is the same as it was originally, and not able to send USB, then the passive adapters won't work, and the active ones suck anyway.
So unless they (or you) switched the board to something newer, no, it won't work.