Tempodivalse:

Imperatives seems to be an exception to this rule.

No, because the implied subject is "vi". You could use an adverb with some imperatives, but the meaning changes like in other cases with explicit subjects; it's not a case of Estas pluve.

I need more elaboration on this. Can I say "estu kuraĝe"? Can I somehow imply that I'm giving and order to a verb? "Scii estu bone" doesn't make much sense to me even though it seems grammatically correct..

WereVrock:I need more elaboration on this. Can I say "estu kuraĝe"? Can I somehow imply that I'm giving and order to a verb? "Scii estu bone" doesn't make much sense to me even though it seems grammatically correct..

It's "estu kuraĝa", with -e it doesn't make any sense.
"scii estu bone" is correct, but you hardly ever have to state "it's good to know" as an order, do you?

Kirilo81:
It's "estu kuraĝa", with -e it doesn't make any sense.
"scii estu bone" is correct, but you hardly ever have to state "it's good to know" as an order, do you?

That is what I'm saying. Was Tempodivalse talking about sentences like "scii estu bone" (knowing shall be good)?

No, with the imperative it's the same as with other forms of the verb: esti/vi estas/estu bona, scii estas/estus/estu bone", agi/vi agas/agu bone...