I’ve commented on the notion of tumblr being censored in that kind of fashion before. On that occasion it was an off the cuff comment and I didn’t bother to look into it to confirm my point of view. This time I have.
A quick look at their archive shows that they haven’t posted anything about this.
Here are a couple of posts on the stuff blog that shed some light on their stance on censorship, from their more general opinion on it, down to indications of exactly what sort of circumstances they feel does warrant censorship.
Whenever you see a post making claims like that floating around the internet, bear in mind that unless the source link actually leads to a post on the staff tumblr that actively states the same thing as the post in its present form, it’s entirely possible that it’s being falsely credited to the staff - or other sources, such as the case may be.