I thought that must be a hoax, but it appears to be real. I don't think it's an official logo, but the T-shirt is on sale on the front page of his campaign's official store:
https://shop.donaldjtrump.com/Even if the resemblance is completely accidental, it's not an excuse. Given the widespread perceptions that he is a bigot, the campaign should be double and triple checking every official release of any kind to make sure there is no reasonable chance that it will be misconstrued. It strains credibility to think that anyone wouldn't recognize that as similar to the emblem of the Nazi party from 1933 to 1945.
(And to be clear, I'm not arguing that it's accidental...I'm just pre-empting that excuse. After all, they already had an ad removed from Facebook (Facebook!) for using a clear Nazi symbol in the last couple of weeks. This isn't the first time something like this happened.)