The typical chiller with hermetic refrigerant motor-compressors will list rated load current (RLA) and/or locked rotor current. Does anyone have a better method for determining a motor HP than thru NEC tables 430.250 and 430.251(B) which are for standard induction motors?

Great question. I also use the tables to estimate the horsepower. Maybe others have a better method?

(My question is probably a stupid one...)
Why do you want the HP of your motor if you already have the RLA? For electrical modeling purposes, usually you do the opposite (from HP to RLA/LRC if only the HP is known).

Now, if you are on the mechanical side of things, then knowing the HP can make some sense (or if you need the torque).

When using the SKM software, the default input is motor HP. The software then models the decaying stator field based on voltage and synchronous speed. The fundamental reason though is that using the RLA to get motor HP from the NEC Tables does not pass the "eyeball" test - meaning a motor compressor with 149 RLA would be 125 HP from the NEC Tables but looks more like a 40 HP induction motor in size.