They certainly can act as a line unit. They will have a higher recon value than any other type of force. As such they will more than likely be allocated to the advance guard during moves by the AI. A force with a high recon value has a positive effect on the determination of the force's overall force ratio viv a vis enemy forces. This is used in the planning and assessment code in numerous places and can affect the likelihood that a force will undertake probes and attacks etc. They do not have a greater probability of detecting enemy in line of sight checks. But that's something I have been considering. It's not there yet though.