After Spectre owned him the first time around, yeah.
KOT is Skyfather+, maybe Elder God level. I just don't know if Atum would be able to absorb him like he did Mephisto and Hela and the others. I want to say no but really there's no telling if it would work or not.
__________________
“Where the longleaf pines are whispering
to him who loved them so.
Where the faint murmurs now dwindling
echo o’er tide and shore."
-A Grave Epitaph in Santa Rosa County, Florida; I wish I could remember the man's name.
Owning Spectre is a nebulous feat. Context and interpretation are usually very subjective, because sometimes he's the 2nd most powerful entity in the DCU, other times he can get punked by Sub-Skyfathers.
I don't know this guy, but he would need more than that to solidify his placement.
Atum is a beast. I dunno if KOT has what it takes. Though, admittedly I don't know enough about him to judge this.
__________________ "Your mother was a venereal disease-ridden prostitute who was raped by the father you never knew and killed herself when she saw what an autistic phaggot you are.
So what about my comments made your ass so sore? Was it me calling you a phaggot? I think not." - Nemebro