Does the rule of "zealots may strike him" also apply to a Kohen zealot?

Question

If a Jewish man and non Jewish woman have relations they are not chayav misa, but if caught while in the act, a 'zealot' (kanoi) may kill them.

A kohen is not allowed to become tomai, so since this law is only a voluntary one, does it also apply to a kohen. Being voluntary it may be more important that he should not become tomai. It is not the same as seeing someone being killed where one has to 'mix' and help even if he will become tomai doing it.

See here that there is some argument in the gemoro if Pinchas was already a kohen. If he was, then it ought to prove that he can. On the other hand since there were others there to do it, it would be unlikely that a kohen should be allowed to and make himself tomai. Maybe that is the reason he told Moshe rabainu to do it.

So it must be that when moshe rabainu told him to do it he already knew that some type of nes (miracle) would happen (like it did in the end) and he would not become tomai.

The site I have now seen and quoted seems to say from rishonim that Pinchas if he was a kohen, he would not have been allowed to kill Zimri. But does not give my answer that he did it on Moshe rabainu's orders. But that he knew somehow a 'nes' would happen but doesnt say how he knew. But there again maybe the only reason was because there were others to do it.

See also this site

Answer 1

In short, it seems to be a machloket, but most mefarshim who address this issue hold that in general a kohen cannot become tamei to fulfill kanna'im pog'in bo:

The Rosh (Peirush ha-Rosh al ha-Torah, Parshat Pinchas) asks this question--how could Pinchas make himself tamei if he was a kohen--and gives 2 answers: Either Pinchas wasn't yet a kohen, or he didn't become tamei, (because they didn't die immediately). The Arukh la-Ner (Sanhedrin 82a) says that Pinchas knew that he wouldn't become tamei, since Moshe told him to perform this action. The Panim Yafot (by the author of the Hafla'ah, Bamidbar 25:7) says that the reason Moshe did not perform the action himself is because he had the status of a kohen gadol, and therefore it wouldn't be permitted for him to become tamei, but Pinchas wasn't yet a kohen. The Kli Chemdah says that Pinchas was allowed to kill Zimri even though he was a kohen because he was saving all of klal yisrael. The Rogachover (Tzofnat Pane'ach Issurei Biah 12:4) says that the reason the chachamim objected to Pinchas's actions (according to the Yerushalmi) was because Pinchas was a kohen, and others could have done it. According to these approaches, in general it would be assur for a kohen to become tamei in such a case.

However, Chavatzelet ha-Sharon (Bamidbar, p. 805) cites the Rogachover (Teshuvot Tzofnat Pane'ach, no. 235) who states that if the halachah of bo'el aramit kanna'im pog'in bo is a chiddush (i.e., something which should be assur but is nevertheless allowed), then it would be allowed for a kohen as well, and the Radak (Shmuel 2:23:20) who writes that Pinchas did become tamei, even though he was a kohen, but that it was mutar because of the mitzvah. According to these (minority) sources, it may be mutar for a kohen as well.

Answer 2

Um ... the Gemara makes it clear that a zealot acting in such a fashion does so at his own risk; had the fornicator turned around and killed the zealot in self-defense, the fornicator would not be charged with murder.

Pinchas was risking getting killed, so I assume he would be willing to risk becoming Tamei. And it appears he felt it necessary to take action himself at that moment.

Regardless, why do you assume he was already a kohen?