I think you have to ask VAC what is the sensitivity of those LEDs to signal voltage. At that point you would only know that your crosstalk is less than the minimum value needed to light up the LED, because the LED is "off", but it won't tell you by how much you're under the minimum signal voltage.
You have to measure the signal voltage in each channel and then calculate crosstalk in db, in order to be able to think about your set-up as compared to some optimum. Typically, a very good well set up cartridge will have the non-driven channel at around -30db with respect to the driven channel, R into L and L into R, at a midband frequency, like 1kHz typically. I think the short answer to your question is "yes and no". It also depends upon your own tolerance for exactitude. How accurate do you want to be?
You have to measure the signal voltage in each channel and then calculate crosstalk in db, in order to be able to think about your set-up as compared to some optimum. Typically, a very good well set up cartridge will have the non-driven channel at around -30db with respect to the driven channel, R into L and L into R, at a midband frequency, like 1kHz typically. I think the short answer to your question is "yes and no". It also depends upon your own tolerance for exactitude. How accurate do you want to be?