If Dillashaw put anymore constraints on this statement then the results would probably be a negative number.
Number of "zero title defense immediate rematches" granted in UFC history: 2.
UFC 49 - Belfort vs. Couture II
Context: Couture lost the title against Belfort due to doctor stoppage via cut eyelid.
UFC 218 - Holloway vs. Aldo II
Context: Aldo replaced an injured Edgar.
Both are technically true and prove Dillashaw's argument as false.
However, Dillashaw would be wrong if he said that the UFC has never granted a champion an immediate rematch. By confining it to a champion with "zero title defenses" it's a lot more limiting to disprove, though based on the above not impossible.
There have been several instances where champions received immediate rematches. The fact of the matter is, Dillashaw got rocked and saved by the bell in his fight against Garbrandt, has a loss against Cruz, and a legitimate and fresh contender in Rivera. The fact that he's trying to argue a case for deserving a fight against DJ (and for the Flyweight title no less) is certainly a great business move, however, it's far from respectable and could be argued as cowardly given that he has two contenders waiting and a third on the way (Garbrandt) if he can get a couple of wins this year.