Sorry I missed this when it first came out; it’s a fascinating question.
A drummer has to find how to fit in with the band’s overall sound. It’s not so much a matter of keeping time - if the band can’t keep time on their own, then the drummer can’t contribute as a musician.
Interesting assignment - listen to bands where the drummer changed and contrast the difference. Pete Best on bootlegs (or in his current life as a nostalgia musician) versus Ringo on the same songs is a good example. Yessongs, the live album, where Alan White had to play some pieces that had originally been done by Bill Bruford. Chester Thompson on the Genesis ‘Seconds Out’, where he had to play stuff that Phil Collins used to play.
Go through a longer lived band like Zappa / The Mothers of Invention or Weather Report and you’ll hear how the whole band changes with the change of drummer.
Sometimes, the drummer is an integral, stand-out part of a band. Can you imagine Rush with anyone other than Neil Peart, or imagine how frustrated Neil Peart would have been in, say, Abba?
Other times, the drummer is not a stand out; he doesn’t solo, he doesn’t try to dominate - think of Charlie Watts in the Rolling Stones, or Levon Helm in The Band. And yet, it’s hard to imagine either group with someone else on the drums.
In jazz, the drummer sets the swing and provides the drive. One of the things I love about Kenny Clarke or especially Art Blakey is the way they egg on the soloist. It’s almost as if when the solo starts to flag or drift, Blakey would come in with a riff as if to say “No, no, son; you’re not finished yet!”
Krupa has already been mentioned, so I won’t belabour that one, but listen for the work of Max Roach, Alvin Jones or Tony Williams, and then listen to the subtlety of Jimmy Cobb on Miles Davis’ ‘Kind of Blue’ - if there were a match for the piano style of Bill Evans, Jimmy Cobb would be it.
So, summing up my long winded opinion, the best drummers integrate themselves into the overall sound of the rest of the band, either stepping into the foreground or by slipping into the groove. It’s not so much about keeping time, it’s about shaping time. There’s a lot more lyricism to drumming than a lot of people give credit for. And lots more to be said on the subject.