The only reason researchers and documentary makers don't perfectly hide themselves is due to how expensive and limited technology is (in Planet Earth they had to setup a hidden blind and stake out an area for months to get the proper footage undetected which is incredibly expensive to do). I imagine if you're a space-faring race capable of visiting planets on a whim, hiding yourself from rather primitive civilizations is trivial, so why wouldn't they?
No, As a general rule we prefer to build giant strip mines on indigenous peoples land; extract all the wealth and generally destroy it.
If Aliens exist and are here; they are not like us at all.
