I believe the concern is probably off-axis phasing. On a theoretical basis, a single point source tweeter should be best, and one tweeter is generally plenty loud. In practice I have not really noticed any degradation from running multiple tweeters in bass cabs. I have experimented with a few bass cabs and always preferred to run both tweeters. But I prefer cabs with extended HF response. There is no guarantee that every bass cab model will work this way. Probably best to experiment and make your own decisions with your own gear.
I have observed nastiness in the high range when various PA cabs are arrayed side by side. In my experience it takes very high-end PA cabs to mitigate this problem. The best I have ever used were Meyer UPA-1P

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Some PA horns produce fairly nasty phasing even when one cab is used.