The State is ambiguous with the yes or no on this subject. Every beer must be properly labeled, so a blank growler can be filled and "tagged" but a lot of breweries don't want to run any risk of crossing the State so most, not all, will only fill their own growlers.
When I went they said they had to sell it with a white birch label so they stuck one on the outside of my growler, but it wasn't hard to take off. Your mileage may vary
I bet they would as long as there isn't a licensing issue, you're still buying their beer! Not sure though.
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