Well first your hardware must have a LED.
Next, led notifications has been in Android since long before gingerbread, so yes gingerbread supports it.
Finally, it's all up to the apps after that. Gmail, messaging, etc have options to make the led flash when you get an email or message. Yet the google+ apps left that option out....
There are apps on the marker that can intercept notifications and make the led flash even when the apps doesn't support it. It's what's integrated in cyanogenmod, since it gives a lot more control over the led notifications.
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