[KDP PUBLISHING] Does KDP Frown Upon Using the Same Interior with Different Covers?

They do for any "Medium Content" book, as it would be considered manipulatiing their search algorithm. So you should not do this with any book that you didn't check the Low Content box and got a free ISBN from Amazon. 

For a low content book, like a journal, notebook, etc. You can do this according to KDP, because things like lined paper are all the same with slight variations.