Unlikely, Remember Deliah said to molly there that she's not your mom, but seriously, which hint that she's isn't even a stepmom. If she was, she would've told her.
I still think Giovanni is most likely his father. He was one of the strongest in Kanto, met Deliah, but seperated from them whan Ash was young when he got Power hungry and evil. Deliah tried to make it that Ash's father Disappeared Mysteriously, he beleived her, and eventually, He's gonna find out if Team Rocket Succeeds in getting Pikachu. But so much time will have passed, Giovanni will have forgotten them and not care anymore (as hinted somewhere between DP abd BF). Then Ash will break in, have a harsh fight, and probably Giovanni will see that Ash is his son. Then a Star Wars cameo will happen and go all wrong. If lucky, Giovanni and Dehlia will Reunite. The End. It's certain to happen