Researchers say space atomic clocks could help uncover the nature of dark matter

It's load of rubbish. The researchers are imagining that dark matter - if it exists - could modify the the frequency of an atomic clock.

Nobody has ever seen this happen, but they wan to spend a lot of money putting an atomic clock on a space-craft that will get closer to the sun that Mercury does in the hope that there will be more dark matter there than there is here.

Of course atomic clocks run more slowly in regions of high gravitational field.

This was demonstrated much more cheaply many years ago with a rather faster clock

Doing gravitational field calculation with all general relativity effects thrown in is extremely tedious, and physicist prefer to explain stuff that isn't simply Newtonian by invoking dark matter. I'm expecting to see it used some time soon to explain the precession of the orbit of Mercury.