Does Hattori Hanzo commit suicide in Kill Bill?

I don't think it's implied that he commits suicide, in any way.

While I'm no expert about traditional Japanese clothing, I think that the garments he wears are typical for the ceremony of the sword and not for suicide.

Also, he doesn't "simply break" his oath. He chooses to make an exception because his honor tells him to. Basically, Bill is Hanzo's former student, and since Bill betrayed his teachings by becoming a contract killer, Hanzo is "forced" to punish him for that, by making and giving The Bride a sword, in order to "fix" the situation. Check the dialogue:

        HANZO       (JAPANESE)
I am retired.

        THE BRIDE       (ENGLISH)
Then give me one of these.

        HANZO       (ENGLISH)
These are not for sale.

        THE BRIDE       (ENGLISH)
I didn't say, sell me. I said, give
me.

        HANZO       (ENGLISH)
And why should I be obliged to
assist you in the extermination of
your vermin?

        THE BRIDE       (ENGLISH)
Because my vermin, is a former
student of yours. And considering
the student, I'd say you had a
rather large obligation.

Hattori Hanzo goes to a dusty window, and writes the name,
"BILL" on it with his finger.

The blonde girl nods her head yes.

She says "Because my vermin, is a former student of yours. And considering the student, I'd say you had a rather large obligation." It's a matter of honor, he's doing this for honor. Committing suicide would "make sense" (in that context) if there was dishonor. Hara kiri is done when you have dishonor and only by committing suicide you'll regain it. It's not the case of Hanzo.

If you prefer I can look for a more clear source, but I think this really makes a point.

I don't think that can be inferred from the scene.

I do remember what you are talking about, and I was taken aback by the staging of the scene. In Japan, white is the color of death. There are only 3 conditions in which a person is clothed in white: (1) they are a corpse, (2) it is a bride (symbolizing her death as her father's child), and (3) a person about to be executed or commit ritual suicide.

However, in the scene it is not just Hanzo who is dressed in white, but Beatrix as well, and obviously she does not commit suicide since we see more of her in future scenes. Therefore, I think that the decisions on costuming were made without a clear understanding of the way white symbolism works in Japan.