Umlaut abuse?

In recently reading an interesting New Yorker article about Tiger conservation in India's Sundarbans Tiger Reserve [1], and noted the following.

He continued, “Fortunately for me, all the six years I stayed there as field director, not a single tiger was killed by the local people—not a single one. It was only due to the coöperation I got.”

Wow; was that umlaut used to indicate the pronunciation of the second oh? Shaken, I googled "umlaut cooperation" to investigate whether this travesty was in common use. Among discussion of previous NY use of the construct in the word reelect, there was mention of the umlaut's use in French (I'm sure the symbol is called something else) to indicate the enunciation of a second vowel sound, e.g., naïve. I'm less offended now, having been familiar only with its sound-changing use in German.

My day will now be unsettled by this personal decision. Do I apply this is everyday writing? After all, NY is probably grammatically snooty, which I also like (to pretend) to be. Faced with readers' (perhaps non-native English speakers) convenience in mind, is the umlaut an acceptable compromise between hyphenation (co-operation?) and suck-it-up-and-remember-the-pronunciation (cooperation), as I would traditionally write?

[1] As a bonus, I had to look up the animal krait, and was reminded by wikipedia of its place in the Kipling short story "Rikki Tiki Tavi", a childhood favourite.