Who really appointed Aharon

I do not normally do this. I have taken a post out of my Torah blog and posted it here as well. The readership on this blog is greater than on the Torah blog so I wanted to present this piece to a wider readership in my search for an answer.. The reason I did so is because this question is really bothering me and I do not have an adequate answer for it. It touches on issues of faith and basics of Judaism, so I felt comfortable including it here as well.

Parshat Korach

Korach had a dispute with Moshe as to who should lead the Jewish nation. He specifically was claiming the right to be Kohen Gadol for himself. We are told by Rashi and the Midrashim that his claim was based on what he felt was a personal slight.
Korach felt that he was skipped over for the Nesius (president or governor perhaps) position of the Kehas tribe in the Levite tribe. How so? Kehas had 4 sons. The eldest was Amram and his two sons took the first two positions, Moshe the leader and Aharon the Kohen Gadol. Next was Yitzhar and his children should have been appointed to the next positions in the food chain of power – the nesius of Kehas. That should then have gone to, so Korach felt, Korach, him being the eldest of Yitzhar’s children. Yet he was not appointed to the position. He was passed over and the job was given to Elitzafan the son of Uziel who was the youngest son of the 4 brothers. He came to claim the Nesius, and once he was making a claim, he changed it to the Kehuna, so he was basically questioning the validity of Moshe’s appointments, based on what he recognized as a bad appointment.
The argument between them proceeds as we all know and the rest of the story is history. In 16:15 after Moshe comes up and presents the terms of the challenge to find out who would be the Kohen, he is then angered by Dasan and Aviram who refuse to come before him for a conciliatory meeting. He turns to God and says a short prayer. He says do not accept their minchot – do not accept the korban they will bring.
I do not understand the purpose of this prayer. Assuming what we believe is true, that Moshe made all his appointments based on the command of Hashem, and nothing involved was personal, what was he davening for? He knew his appointments had been directed by God and by definition Hashem would only accept Aharon’s korban, and would not accept Dasan, Avirams or any of the other 250 people involved in the dispute! Hashem could not because they would have been bringing the korban inappropriately and would have to be killed like Nadav and Avihu had been killed. I understand why the people went ahead with it. They doubted Moshe and were challenging him. I do not understand Moshe – just by the very nature of his position and actions, he should have been confident of his victory over this uprising. Why would he feel the need to offer a special prayer for his victory?
Yes, I know Rashi says he was referring to other korbanos – not to accept any of the korbanos presented by these people, but that is hard to swallow as an answer – Moshe knew they were all about to be killed and would not be offering any more korbanot. It could be Rashi was bothered by the same question and felt the need to explain it referring to other korbanot, but I think that is an insufficient answer to my question.
If you have any suggestions and possible answers, please post it in the comments, or email me at Israeli.jew@gmail.com – this question has been disturbing me for a few days now and I have not thought of a satisfactory answer.