It really depends on what exactly is the scope of your training with the Millers and also how you are using your Lincolns both in production and quality control
The Live Arc system is quite good and if you are looking at technique, (gun angle) and parameter control than you can probably program the Millers to perform in the parameter ranges (nearly) that your Lincolns are doing in production.
If you are using PowerWave platform Lincolns than Live Arc could training data could be compared to Lincoln Checkpoint cloud based data (if you are using it) and really get some bang.
If all this debate is simply over a demo? Just do it. It will be fun and open your eyes to some process control possibilities that can be gotten with either Lincoln or Miler data monitoring in production.
The only confusing differences will be if you're using GMAW-P, as the transfer mode type names and pulse control setting names/numbers will be different.
For example, Miller Axcess machines have Pulse waveforms called Accu-Pulse, Accu-Curve, RMD, etc.
Lincoln has Rapid Arc, Rapid X, STT, etc.
For pulse controls Miller Axcess has Arc Adjust in range from 0-99, and Arc Control in range from 0-50.
Lincoln Power Wave has Trim in range from .50 to 1.50 and Wave Control in range from -10 to +10.
Option names on different power sources can change as well.
The point is that simple instruction to the Welders will be needed to clarify options and setting numbers.