On my trader, I have a /setmsg that goes something like "Pirate spotted! Full power to engines, all hands to battlestations!"
If I get dropped out of a lane by a pirate, I'll hit the setmsg and start running. That gets my point across, and lets the other player know that yes, I am here, and will be attempting to get away now. If the pirate CDs me and stops me, then I'll continue typing out RP from there. If not, and I'm trying to get away and he's talking to me, I'll hit the cruise engines or thrusters and type while still trying to get away.
On my pirate, I have a /setmsg that goes like "You there, trader! Stop your ship, this is a piracy!" When I drop a trader out of a lane, I'll hit the message, then figure out how much to charge the guy for safe passage. Again, it's a quick message that allows me to initiate an RP without being easy gun-bait. I think this is certainly acceptable use of the /setmsg feature.
