J.N.
As long as he takes a few ounces from a bottle, I think he would be ok. If you leave him with a sitter and he is hungry, he will at least accept the bottle enough to hold him over till you get home. Same with Dad.
Just keep giving him a bottle a few times a week. And I agree with the other response that said go back to the slower flowing nipple -- the breast is slower than most bottles and he probably dislikes the difference.