Reverend Mothers are connected with their female ancestors. Paul and Leto have access to both male and female ancestors. What’s the explanation for Alia’s communication with Agamemnon and Vladimir Harkonnen?
It seems yes, but uncontrolled.
As you note, Alia was able to communicate with male ancestors, in particular the Baron. This was always the goal of that particular branch of the Bene Gesserit breeding program - a Kwisatz Haderach who, as well as infaliable prescience, could communicate with both the male and female ancestry line.
However, Alia lacked control. This could be down to three things -
- She was always the next "intended" branch in the Kwisatz Haderach program, not Paul. Had she had a child by Feyd (always the intention) then that child would be the Kwisatz Haderach. Like Paul, this meant that she had latent abilities, but not perfect control over them.
- Again, like Paul, she was not expected to have these abilities nor trained formally by the Bene Gesserit in their uses. Unlike Paul however, she did exhibit them much, much earlier (what with a two-year-old having adult conversations and stabbing people.)
- She was exposed and awoken to her "ancestral memories" in the womb during Jessica's taking of the water of life.
All this combines to make Alia very much a tinderbox, or a wildcard. She was essentially pretty close to being a Kwisatz Haderach in the breeding program, and everything that happened basically spun her out enough that she gained the memories of at least some of her male ancestors, but not the control, and it's doubtful that the Atreides court would have realised and made time/trusted for the Bene Gesserit to intervene (plus Jessica more or less ran back to Caladan as soon as she could.)