The original rules said, "A wizard can see through the eyes of [...] illusions brought by his creation spells." (AW 4) There's a long section following on the limitations of illusions but it says nothing about vision. In the Legacy Beta version, this line has been copied verbatim on p137. I think it's fairly clear the intent is that it is possible to use an illusion as a scout. To say that the intent is that the illusion can only show you what you already know about is to make the ability a useless humorous mockery, a lot like Invisible Boy's power to be invisible only when nobody is watching (Mystery Men). There's no reason I know to think this was what was intended and it seems like the sort of thing that would be mentioned.
The idea that illusions can only see things the wizard knows about is, IMO, absolutely in the spirit of illusions. When I GM, I say illusions can't be used as scouts. But I think it's pretty clear that's a widely-used house rule, and in RAW they can.
I think the decision was driven by the designer believing that the ability to see through the eyes of a summoned creature was cool (see the last paragraph of the battle in Wizard) and perhaps realistically required if the illusion was to be teleoperated in combat.
Curiously, there's nothing in the rules saying that an illusion can hear or smell, though it seems in the spirit of the rules to think this should work the same as vision.
I think it's an open question whether illusions and other created figures should have enough intelligence to operate independently. Perhaps some or all of them should be smart enough the wizard could say, "run around the corner and kill whatever you find." This could be a magical talent, or a more advanced version of the spell.