GMSL1 has both forward and reverse data. A customer would need to use high impedance probes and use filtering to take out only the forward or reverse data. As GMSL is a proprietary link, there is not much use for checking items beyond the PHY level (rise/fall time, output amplitudes, etc.)
It is better to check for decode/PRBS errors (forward channel) or compare control channel data on UART/I2C pins on both ends of the GMSL link (reverse channel).