Nope. It's canon.
The DLC was bad, awful, the gameplay was truly horrible.
And they didn't do a good job at writing the story either, so the aliens just came out as psychopathic pricks.
But I'll still consider it canon.
Just cause the game design is bad and the story is very black and white doesn't mean it's not canon really.
And is there a law in the gaming industry that an easter egg cannot become canon?
I think not.
Next DLC: Godzilla vs Doctor Who.
If you were thinking I was referring to Mothership Zeta, I wasn't. I was referring to the crashed UFO and a terminal that says the pre-war government was aware a UFO crash landed but couldn't find it in dense forest.
Zeta is the only DLC I did not get, due to the fact pretty much every review was awful and I personally feel aliens have no place in the Fallout universe.
As for the DLC, I recall somewhere that Beth made it for giggles rather than taken serious. That said, the DLC does not automatically means its canon or that the event took place. I can pretty much say the same for every DLC made by Beth (save Broken Steel and Shivering Isle) is all optional as to what the PC did and not do, but it does not automatically mean its canon.
It's my opinion that if a development company releases official DLC for a game released by the same company it would be considered canon. Not to purposely get off topic but an example of non-canon or spinoff, or however you'd like to phrase it, would be the game Fire Warrior being called canon to the Warhammer 40k universe because Games Workshop had nothing to do with it's development, it just fits under an umbrella of 40k as a whole.