I would argue that you should capitalize 'Em when it appears in the middle of a title.
Style / Language / English: "Capitalize contractions and slang consistent with the rules above to the extent that such clearly apply. For example, do not capitalize o’ for “of”, ‘n’ or n’ for “and”. "
My amateur opinion as a native speaker of English, but not trained in details of English orthography:
No, do not capitalise. Why? 'em is a contraction of Them. The initial letter of the full word is what would be capitalised. But that initial letter is removed by the contraction. The result: no initial letter, no capital.
Also, the mark that looks like a quote mark should be a 9, not a 6. That is because the 9-shaped quotation mark indicates a contraction.
So, the capitalisation should be Make ’em Pay. In my humble opinion.
P.S. to type the 9-shaped quotation mark easily, type a temporary letter before the quotation mark, then the quotation mark (which will come out 9-shaped), then the contraction; then delete the temporary letter. e.g. x → x’ → x’em → ’em .
By the way, I prefer to use U+02BC (MODIFIER LETTER APOSTROPHE) for apostrophe rather than U+2019 (RIGHT SINGLE QUOTATION MARK), because an apostrophe is not a quotation mark – but the Unicode committee made a mess of this.
Is this “consistent” with the rules above? What does “consistent” mean in this context? To what extent do these rules “clearly apply”? What is “clearly” vs not “clearly” in this context?
I’m afraid I don’t read that style rule as giving us very much help. And intuitively, reading as a native English speaker, Make ’em Pay looks more correct than Make ’Em Pay, to me; if the style rule points to a different result, I’d argue that the style rule needs tweaking.
I’d say yes according to the guidelines, but AFAIK most editors keep ’em lowercase. In part, this would be because of the guess case algorithm. My opinion is that words with their first letter elided should be lowercase, except in cases where the word is clearly stressed, such as in She’ll Be Coming ’Round the Mountain.