Yes. The other person's belief has no bearing on whether spiritual energy work is effective — the ritual is directed at the emotional and energetic connection between two people, not at convincing anyone that magic is real.
Think of it the way you'd think about someone changing their mind about you gradually, without ever being told why: they simply start noticing you differently, thinking of you more, or feeling drawn to reach out. Most clients tell me the other person has no idea a casting was even done.
What does matter is accuracy — I need their correct name and, ideally, a birth date or photo, so the work is directed at the right person and not diluted.