The Chizkuni Bireishis 25:8 says at the end of his comment that Esav also did Teshuva. Is there other sources for this amongst the Rishonim and Chazal?
When Jacob met Esau he provided him with gifts. According to Abarbanel (Gen. 33: 1-17), these gifts served as Jacob's blessings. Although Jacob took Esau's blessing from Isaac, he was now bestowing his own blessings onto Esau, making them equals. If Jacob felt that Esau was undeserving of the blessing, he would not have given it to him. Also, a Midrash makes use of the story when Isaac and Ishmael bury Abraham. The Midrash says that Ishmael performed teshuvah, repentance. (Gen. Rabbah 30:4, 38:12, BT Bava Batra 16b). We might also apply this reunion of brothers to the Jacob and Esau reconciliation to mean that Esau also did teshuvah as well.
I think the Medrash in Beraishis Rabah Chapter 67 [end - 13] does say that he considered to maybe do teshuvah. But I don't think it says that he actually did.
Even if he did, he might of afterwards returned to his evil ways.
Also, there are many different levels of teshuvah. Just like there are many different levels of tzadikim and reshaim. The Medrash is pretty clear that he did not do any major teshuvah, since he kept his other bad wives. Unless you say that that part of the Medrash is arguing on the first part.
The Kook edition of Chizkuni leaves out the part of Eisav doing teshuva.