While non-intellignet causes have been considered for the basic, circular "crop circles" it is true that most are considered the result of intelligent work.
However so far as I am aware science has NOT concluded that any unknown intelligence is involved. Even though there is no non-design explanation that is currently adequate to explain the more complex examples or any real hope of one.
So yes, I'd say that this is an interesting comparions - the ID movement IS very like the people who insist that crop circles are the work of extraterrestrials. And the ID'ers appear to come off worse in that comparison.
Well lets clarify a few things. Human pranksters are a known intelligence - we know that they exist even if we can't name individuals responsible for a particular circle.
And I would certainy say that the more complex patterns are both more obviously the product of design than anything in biology - and the lack of a reasonable alternative is more solid than for anything in biology.
So in fact - especially if we include the possibility of human pranksters the inference of intelligent design has a stronger basis for crop circles than anything the ID movement has.
Now I don't think that there has been a lot of solid scientific investigation of crop circles. And that is the main reason why there has been no solid conclusion - it's just too likely to be human pranksters and that is of zero scientific interest (an unknown or poorly understood weather phenomenon on the other hand would be - so the more complex patterns are really LESS interesting to science).
In principle it is POSSIBLE some form of "ID" might become science - but the ID movement would need to seriously clean up its act and start doing a lot more work before there is any hope that they will contribute to it. It is NOT very likely that a scientific "ID" would bear much resemblance to what we see from the current movement.