Do I still honor my mom's wishes to not see her other child even now that she is on hospice?

NO NO NO! You will have a hysterical person on your hands. Maybe a note or letter from said child that you could read to her. But physically my answer would be Heck NO!

Nah screw him. I have a sister similar to this and if she comes skulking around trying to see my mom after decades of estrangement, well, it's not going to go well. So done. She deserves nothing and that's what she'll get.

See what he want - tell his wife you want to talk to him. That may give you an idea of his agenda, enough that you know it is not safe to proceed. If he is sounding somewhat calm, expressing regrets and desire to see mom one last time.....maybe it will work.
See what your mother wants. Lots of emotions are swirling as the end of life approaches, and she may want to see him again. Even if she can't articulate why she wants to see him, or if she leaves it up to you, I'd think hard about giving him a very brief visit, set at your convenience, with a friend as a witness. You can call 911 to have him removed the minute he acts up.
If she is clear that she does not want to see him, then that is your answer.
I've seen enough situations of reconciliation/forgiveness etc at end of life, even in families that were adamant that a particular person be excluded for good reasons.
A hospice social worker and chaplain can be good sounding boards for this decision, may be able to be present, etc.

If she says no than do not bother. But if she says yes, I would not tell him she is on hospice except that the doctors are doing all that they can for her. Hide all of the literature and drugs if he visits. I suggest you have a trustworthy friend of caregiver for a limited visit so that you have no contact. You can give instructions to the caregiver not to mention hospice.
You might also video her and ask if she wants a visit to confirm that she said no.

No. Just No.

We cannot make up for a lifetime of a bad relationship in one visit. Your mother deserves peace.

My OB was not allowed to see daddy before he died. For daddy's sake.

Honor her wishes. Making sure she is safe from harassment and strife is one of the last things you can do for her.

You don't have an obligation to inform anyone she's in hospice. That qualifies as private medical information if you want it to be. You owe no one explanations of your caregiving; you're doing your best.

Focus on your mom. Let her know she is loved and safe from anything that would harm her.

I wish her a safe passing, and peace to you.

This is when you wish that you were an only child, right?

What is the purpose of his visit? To stir up more trouble for you? If you sense that is what it is about, then why should he visit?

Plus, if his visits will be distressing for your mom and she doesn’t want to see him honor her wishes.

Why can’t he speak for himself instead of having his wife call you? Anyway, tell his wife the same thing as you would tell him.

Best wishes to you and your mother.

Ask yourself who the visit is supposed to benefit - if it is just to sooth his conscience and neither you or your mother would gain anything positive from it then no, let him reap what he has sewn.

Are you POA? Then you handle it as POA. You ask your Mom if she wishes to see him. If he says no then no is the answer. If she cannot answer then protect her from him as she asked you to. If your Mother doesn't want him to visit, and he is threatening to do so, then you as POA should file in court for a restraining order. If he visits with APS or anyone else it should be accompanied. And be ready to dial 911.

No don't let him see her. He's done enough. She deserves to die in peace.