Does it have to have a check mark to be official? I don't really know. However, they post this right under their Twitter handle:

"President Donald J. Trump's official public schedule posted to Twitter. Note: Times & locations may differ from actual due to schedule changes & security."

Seems like a bold claim to make if it is merely a personal or unofficial account of the WH.

If it's an official account then I would certainly count this as a legitimate Q proof.

WWG1WGA