Gimbals/turrets are still able to fire and hit you, even though you can't be targeted, by untargeting you/using forward fire function.
Against NPC ships, Silent Running isn't very useful at all. They don't seem to have trouble aquiring your ship.
AI has trouble scanning you when you drop below 20% heat, that's why heat sinks are just as effective for breaking scans.
A couple more things about Silent Running:
The closer you get to your opponent, the less effective it is. I can't remember if its 200m or 500m, but once you're within that range, you'll still appear on radar. EDIT: After thinking about it a bit I believe it has something to do with how good the sensors are. So a ship with 6A sensors can pick up a stealth ship on radar further out than a ship with 4D sensors.
Night vision makes spotting you easy if you stay in line-of-sight.
You'll appear on your target's radar (and be targetable) while firing on them.
There is an engineering modification for laser weapons called emissive, which enhances your signature if you're hit by them. It's the bane of Silent Running builds.