Indeed it is! I think that the measurement method you describe is used by the likes of RCCB's (Residual Current Circuit Breakers), but I believe LIM's actually inject a small test current and measure voltage modulus/phase angle to work out the impedance of each 'line' to ground....see here for example: How_it_Works
In other words, it doesn't actually measure actual leakage current as directly as the EST (which is what you said)!

Perhaps the laser equipment actually has a particularly high leakage current, and is not indicative of a fault as such. Whether it is wise to use in a patient environment..well, that is another question entirely!