I don´t think Darkseid can do anything about Dagoth Ur. Dagoth Ur has true-godly regen, abstract existance (Type 2), many different types of immortality that Darkseid cannot deal with (Types 5, 8, and 9), and acasuality (Type 4). Not only that, but Dagoth Ur has either similar or same abilities as Darkseid, along with more that once again, Darkseid can deal with like reality warping, casuality manipulation, physics manipulation, statistics amplification, and many more.
Although, if this battle is taking place within The Red Mountain (which I think it is), there could be a possibility Darkseid could somehow server ties between Dagoth Ur and The Heart of Lorkhan. Although, I sort of doubt this.