Are any of the Mass Effect 1 DLCs relevant to the story in Mass Effect 2?
Solution 1:
Mass Effect 1's "Bring Down the Sky" has an effect in Mass Effect 2 and 3. The other available DLC, "Pinnacle Station", does not.
You've asked to avoid spoilers, so I'll simply say that the default canon is that Bring Down the Sky ends with the Renegade ending. If you play it personally, you can alter this.