BMS doesn't have any HARM slaving capability to JHCMS that I'm aware of, but it does have the HARM Targeting System (HTS) which is like cheating. It gives you the HARM Attack Display (HAD) which is a top down view of the battle space with all emitting radars, with their type, and color coded based on threat level and strength of emissions. It also gives you a handy bubble that shows you exactly what's in range of the HARM. See something red or yellow on the HAD that you want dead? TMS up, make sure it's in the HARM bubble, magnum. It's much easier than trying to use HARM As Sensor (HAS) or the various POS mods (EOM, PB and RUK).
The Hornet does not have the HTS, that's an air force system. It has the same HAS modes as the Viper (because the HARM itself provides them), and from my understanding it has a Navy system that is somewhat similar to the HTS but not as advanced. I don't know much about it, but I'm excited to learn once we get HARMs.
This is what the HAD looks like in the Viper: